Stage in fix for toolsetRunner test (#9086)

Ensure this test doesn't start failing when I merge
swiftlang/swift-build#765

Author: owenv

Tests/CommandsTests/TestCommandTests.swift

@@ -124,6 +124,7 @@ struct TestCommandTests {
     ) async throws {
         try await withKnownIssue(
             "Windows: Driver threw unable to load output file map",
+            isIntermittent: true
         ) {
             try await fixture(name: "Miscellaneous/EchoExecutable") { fixturePath in
                 #if os(Windows)