[test] Disable another measure method missed previously on Linux

On macOS since there is an override, both `measure` methods funnel
through one entry point, but on other platforms they are not `open`, so
we need to shadow all of them.

Author: benlangmuir

Sources/SKTestSupport/PerfTestCase.swift

@@ -45,6 +45,9 @@ open class PerfTestCase: XCTestCase {
     {
       block()
     }
+    public func measure(block: () -> Void) {
+      block()
+    }
   #endif
 #endif