Fixed test script handling of unknown/additional args

[bvaughn]

Using multiple pass-through args (e.g. a test filter and a --watch flag) like so:

yarn test ReactHooksWithNoopRenderer --watch

Was being incorrect handled like so:

$ node ./scripts/jest/jest-cli.js ReactHooksWithNoopRenderer --watch
$ NODE_ENV=development RELEASE_CHANNEL=experimental node ./scripts/jest/jest.js --config ./scripts/jest/config.source.js ReactHooksWithNoopRenderer,--watch

Running tests for default (experimental)...
No tests found, exiting with code 1
Run with `--passWithNoTests` to exit with code 0
In /Users/bvaughn/Documents/git/react
  1116 files checked.
  roots: /Users/bvaughn/Documents/git/react/packages, /Users/bvaughn/Documents/git/react/scripts - 1116 matches
  testMatch:  - 0 matches
  testPathIgnorePatterns: /node_modules/ - 1116 matches
  testRegex: /__tests__/[^/]*(\.js|\.coffee|[^d]\.ts)$ - 260 matches
Pattern: ReactHooksWithNoopRenderer,--watch - 0 matches

This PR fixes that.

[bvaughn]

(argv._ is an array of additional args.)

[rickhanlonii]

Whoops nice catch

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