CI test fixup

Author: cachemeifyoucan

Tests/SwiftDriverTests/ToolchainTests.swift

@@ -193,7 +193,9 @@ import CRT
     #endif
     let SWIFT_FRONTEND_EXEC = ProcessEnvironmentKey("SWIFT_DRIVER_SWIFT_FRONTEND_EXEC")
     let SWIFT_SCANNER_LIB = ProcessEnvironmentKey("SWIFT_DRIVER_SWIFTSCAN_LIB")
-    let baseEnv = ProcessEnv.block
+    var baseEnv = ProcessEnv.block
+    baseEnv.removeValue(forKey: SWIFT_FRONTEND_EXEC)
+    baseEnv.removeValue(forKey: SWIFT_SCANNER_LIB)
     #if os(Windows)
     let separator = ";"
     #else