Fully-qualify reference to 'Comment' type in #expect expansion when comment argument isn't a string literal (#1645)

This fixes a build error which can arise in the code emitted by
`#expect` when the `comment` argument is not a string literal and the
module the `#expect` appears in has a custom type visible named
`Comment`, conflicting with the testing library's built-in type by that
name.

Fixes #1641

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: stmontgomery

Sources/TestingMacros/ConditionMacro.swift

@@ -177,7 +177,7 @@ extension ConditionMacro {
         // the resulting comment array.
         checkArguments.append(Argument(
           label: "comments",
-          expression: #"(\#(commentsArrayExpr) as [Comment?]).compactMap(\.self)"#
+          expression: #"(\#(commentsArrayExpr) as [Testing.Comment?]).compactMap(\.self)"#
         ))
       } else {
         checkArguments.append(Argument(label: "comments", expression: commentsArrayExpr))

Tests/TestingTests/MiscellaneousTests.swift

@@ -637,4 +637,14 @@ struct MiscellaneousTests {
     }
     #expect(duration < .seconds(1))
   }
+
+  @Test func `Expectation with a non-string literal comment and ambiguous 'Comment' type`() {
+    let comment: Comment = "foo"
+    do {
+      // Declare a custom type whose name conflicts with the testing library's
+      // built-in Comment type.
+      struct Comment {}
+      #expect(true as Bool, comment)
+    }
+  }
 }