CT: Speed up phet-io build tests by omitting copySupplementalPhetioFiles logic

[zepumph]

This issue is a superset of the linked checkbox in https://github.com/phetsims/phet-io/issues/1664. Part of this process is to generate the phetio api, which kicks off puppeteer and can take upwards of 5 seconds per build. If we don't need this logic for a test, then CT could benefit from this speed increase.

insert large numbers about how often builds occur on CT here

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For anyone else reading this, "copySupplementalPhetioFiles logic" is apparently copySupplementalPhetioFiles.js, which is used in buildRunnable.js.