Test: Guard a ManifestSourceGenerationTest and annotate skip message (#8582)

Guard a test in ManifestSourceGenerationTest based on the compiler
version, and annotate skipped tests with a GitHub issue.

Also, enable the two Workspace Traits tests that were added after #8569
was merged.

Relates to: #8433
Issue: rdar://148248105

Author: bkhouri

Sources/_InternalTestSupport/XCTAssertHelpers.swift

@@ -101,6 +101,13 @@ public func XCTRequires(
     }
 }
 
+public func XCTSkipIfCompilerLessThan6_2() throws {
+    #if compiler(>=6.2)
+    #else
+        throw XCTSkip("Skipping as compiler version is less thann 6.2")
+    #endif
+}
+
 /// An `async`-friendly replacement for `XCTAssertThrowsError`.
 public func XCTAssertAsyncThrowsError<T>(
     _ expression: @autoclosure () async throws -> T,

Tests/WorkspaceTests/ManifestSourceGenerationTests.swift

@@ -796,7 +796,7 @@ final class ManifestSourceGenerationTests: XCTestCase {
     }
 
     func testStrictMemorySafety() async throws {
-        try XCTSkipOnWindows(because: "compilation error:  type 'SwiftSetting' has no member 'strictMemorySafety'")
+        try XCTSkipIfCompilerLessThan6_2()
 
         let manifestContents = """
             // swift-tools-version:6.2
@@ -865,7 +865,7 @@ final class ManifestSourceGenerationTests: XCTestCase {
     }
 
     func testDefaultIsolation() async throws {
-        try XCTSkipOnWindows(because: "there are compilation errors")
+        try XCTSkipOnWindows(because: "https://github.com/swiftlang/swift-package-manager/issues/8543: there are compilation errors")
 
         let manifest = Manifest.createRootManifest(
             displayName: "pkg",

Tests/WorkspaceTests/WorkspaceTests.swift

@@ -16145,8 +16145,6 @@ final class WorkspaceTests: XCTestCase {
     }
 
     func testInvalidTrait_WhenParentPackageEnablesTraits() async throws {
-        try XCTSkipOnWindows(because: #"\tmp\ws doesn't exist in file system"#)
-
         let sandbox = AbsolutePath("/tmp/ws/")
         let fs = InMemoryFileSystem()
 
@@ -16208,8 +16206,6 @@ final class WorkspaceTests: XCTestCase {
     }
 
     func testInvalidTraitConfiguration_ForRootPackage() async throws {
-        try XCTSkipOnWindows(because: #"\tmp\ws doesn't exist in file system"#)
-
         let sandbox = AbsolutePath("/tmp/ws/")
         let fs = InMemoryFileSystem()