Add 6.3 into the testing matrix. (#2012)

Move the linage test to "latest", don't think we are going to track this
for every release where it could be possible.

.github/workflows/build.yml

@@ -23,7 +23,7 @@ jobs:
         # Looking at https://hub.docker.com/_/swift, the version only tags (i.e. - 6.1)
         # could use different Ubuntu releases. At the moment they are all the "noble",
         # which is also what would be desired, so we don't bother listing explicit ones.
-        swift: ["6.2", "6.1", "6.0"]
+        swift: ["6.3", "6.2", "6.1", "6.0"]
         traits: ["default", "disable-default-traits", "BinaryDelimitedStreams", "FieldMaskUtilities"]
 
         exclude:
@@ -76,7 +76,7 @@ jobs:
     runs-on: ubuntu-latest
     name: Foundation linkage test
     container:
-      image: swift:6.2
+      image: swift:latest
     steps:
     - name: Checkout
       uses: actions/checkout@v6
@@ -89,7 +89,6 @@ jobs:
       run: apt-get update && apt-get install -y g++
     - name: Run linkage test
       run: ./scripts/run-linkage-test.sh
-    
 
   api-breakage:
     name: Api Breakage Compared to main branch