[TEST-ONLY] Fix CASPath in swiftCachingSwiftPM()

Change CASPath used in `swiftCachingSwiftPM` to be in the temp directory
like the other tests. Current path might be complained by certain OS
configuration about permission issues.

Author: cachemeifyoucan

Tests/SWBBuildSystemTests/SwiftCompilationCachingTests.swift

@@ -191,7 +191,7 @@ fileprivate struct SwiftCompilationCachingTests: CoreBasedTests {
                             "PRODUCT_NAME": "$(TARGET_NAME)",
                             "SWIFT_ENABLE_COMPILE_CACHE": "YES",
                             "COMPILATION_CACHE_ENABLE_DIAGNOSTIC_REMARKS": "YES",
-                            "COMPILATION_CACHE_CAS_PATH": "$(DSTROOT)/CompilationCache"])],
+                            "COMPILATION_CACHE_CAS_PATH": tmpDirPath.join("CompilationCache").str])],
                         buildPhases: [
                             TestSourcesBuildPhase(["App1.swift"]),
                             TestFrameworksBuildPhase([TestBuildFile(.target("FooProduct"))])],