Fix web worker issue caused by the CSP using Safari in dev mode

What does this MR do and why?

Because Safari doesn't support worker-src in the CSP, it falls back to child-src. In !71345 (merged) 'self' was removed from child-src so some pages that use web workers started failing in Safari.

@kassio reported issues in https://gitlab.slack.com/archives/CETG54GQ0/p1634725253297800 (internal)

Screenshots or screen recordings

No visible changes

How to set up and validate locally

Run the GDK and using Safari visit an MR page and/or a Web IDE page. Navigate the application in general and keep an eye on the developer console for CSP-related errors being logged.

MR acceptance checklist

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