[HIR] fix missing read reference to switch test value

Unless I'm mistaken, the switch operand is missing here.

compiler/forget/src/HIR/InferReferenceEffects.ts

@@ -641,6 +641,7 @@ function inferBlock(env: Environment, block: BasicBlock) {
       break;
     }
     case "switch": {
+      env.reference(block.terminal.test, Effect.Read);
       for (const case_ of block.terminal.cases) {
         if (case_.test !== null) {
           env.reference(case_.test, Effect.Read);

compiler/forget/src/__tests__/fixtures/hir/reverse-postorder.expect.md

@@ -43,7 +43,7 @@ bb2:
   [2] Const mutate $8 = 2
   [3] Const mutate $9 = 1
   [4] Const mutate $10 = 0
-  Switch (<unknown> props$6.test)
+  Switch (read props$6.test)
     Case read $10: bb8
     Case read $9: bb6
     Case read $8: bb4

compiler/forget/src/__tests__/fixtures/hir/ssa-switch.expect.md

@@ -33,7 +33,7 @@ bb0:
   [3] Const mutate $12 = Binary read x$10 === read $11
   [4] Const mutate $13 = 1
   [5] Const mutate $14 = Binary read x$10 === read $13
-  Switch (<unknown> x$10)
+  Switch (read x$10)
     Case read $14: bb5
     Case read $12: bb3
     Default: bb2

compiler/forget/src/__tests__/fixtures/hir/switch-non-final-default.expect.md

@@ -37,7 +37,7 @@ bb0:
   [3] Const mutate $12 = false
   [4] Const mutate $13 = true
   [5] Const mutate $14 = 1
-  Switch (<unknown> props$9.p0)
+  Switch (read props$9.p0)
     Case read $14: bb1
     Case read $13: bb6
     Default: bb1

compiler/forget/src/__tests__/fixtures/hir/switch.expect.md

@@ -32,7 +32,7 @@ bb0:
   [2] Let mutate y$10 = undefined
   [3] Const mutate $11 = false
   [4] Const mutate $12 = true
-  Switch (<unknown> props$8.p0)
+  Switch (read props$8.p0)
     Case read $12: bb4
     Case read $11: bb2
     Default: bb1