Don't perform V8 instrumenting if !collectCoverage

If `coverageProvider: "v8"` is provided in the Jest config, then the
overhead of V8 instrumenting occurs, even if `collectCoverage: false`.

This saves about ~100ms of Jest-invocation-time on my machine.

packages/jest-runner/src/runTest.ts

@@ -270,6 +270,7 @@ async function runTestInternal(
 
   // if we don't have `getVmContext` on the env skip coverage
   const collectV8Coverage =
+    globalConfig.collectCoverage &&
     globalConfig.coverageProvider === 'v8' &&
     typeof environment.getVmContext === 'function';