Drop Swift 6.0 (#61)

Motivation:

Swift 6.0 is no longer supported, we should bump the tools version and
remove it from our CI.

Modifications:

* Bump the Swift tools version to Swift 6.1
* Remove Swift 6.0 jobs where appropriate in main.yml, pull_request.yml

Result:

Code reflects our support window.

.github/workflows/main.yml

@@ -14,7 +14,6 @@ jobs:
     name: Unit tests
     uses: apple/swift-nio/.github/workflows/unit_tests.yml@main
     with:
-      linux_6_0_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
       linux_6_1_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
       linux_6_2_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
       linux_6_3_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"

.github/workflows/pull_request.yml

@@ -18,7 +18,6 @@ jobs:
     name: Unit tests
     uses: apple/swift-nio/.github/workflows/unit_tests.yml@main
     with:
-      linux_6_0_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
       linux_6_1_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
       linux_6_2_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"
       linux_6_3_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error -Xswiftc -require-explicit-sendable"

Package@swift-6.0.swift

@@ -1,64 +0,0 @@
-// swift-tools-version:6.0
-//===----------------------------------------------------------------------===//
-//
-// This source file is part of the SwiftOpenAPIGenerator open source project
-//
-// Copyright (c) 2023 Apple Inc. and the SwiftOpenAPIGenerator project authors
-// Licensed under Apache License v2.0
-//
-// See LICENSE.txt for license information
-// See CONTRIBUTORS.txt for the list of SwiftOpenAPIGenerator project authors
-//
-// SPDX-License-Identifier: Apache-2.0
-//
-//===----------------------------------------------------------------------===//
-import Foundation
-import PackageDescription
-
-// General Swift-settings for all targets.
-let swiftSettings: [SwiftSetting] = [
-    // https://github.com/apple/swift-evolution/blob/main/proposals/0335-existential-any.md
-    // Require `any` for existential types.
-    .enableUpcomingFeature("ExistentialAny")
-]
-
-let package = Package(
-    name: "swift-openapi-async-http-client",
-    platforms: [.macOS(.v10_15), .iOS(.v13), .tvOS(.v13), .watchOS(.v6), .visionOS(.v1)],
-    products: [.library(name: "OpenAPIAsyncHTTPClient", targets: ["OpenAPIAsyncHTTPClient"])],
-    dependencies: [
-        .package(url: "https://github.com/apple/swift-nio", from: "2.58.0"),
-        .package(url: "https://github.com/swift-server/async-http-client.git", from: "1.23.0"),
-        .package(url: "https://github.com/apple/swift-openapi-runtime", from: "1.0.0"),
-        .package(url: "https://github.com/apple/swift-http-types", from: "1.0.0"),
-    ],
-    targets: [
-        .target(
-            name: "OpenAPIAsyncHTTPClient",
-            dependencies: [
-                .product(name: "OpenAPIRuntime", package: "swift-openapi-runtime"),
-                .product(name: "HTTPTypes", package: "swift-http-types"),
-                .product(name: "AsyncHTTPClient", package: "async-http-client"),
-            ],
-            swiftSettings: swiftSettings
-        ),
-        .testTarget(
-            name: "OpenAPIAsyncHTTPClientTests",
-            dependencies: ["OpenAPIAsyncHTTPClient"],
-            swiftSettings: swiftSettings
-        ),
-    ]
-)
-
-// ---    STANDARD CROSS-REPO SETTINGS DO NOT EDIT   --- //
-for target in package.targets {
-    switch target.type {
-    case .regular, .test, .executable:
-        var settings = target.swiftSettings ?? []
-        // https://github.com/swiftlang/swift-evolution/blob/main/proposals/0444-member-import-visibility.md
-        settings.append(.enableUpcomingFeature("MemberImportVisibility"))
-        target.swiftSettings = settings
-    case .macro, .plugin, .system, .binary: ()  // not applicable
-    @unknown default: ()  // we don't know what to do here, do nothing
-    }
-}// --- END: STANDARD CROSS-REPO SETTINGS DO NOT EDIT --- //