Change REPL artefact generation so that browser build will work on CI

[lukastaegert]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

Description

This is a small change to the CI process for Rollup 2 so that the Rollup 3 browser build is able to generate REPL artifacts on CI even before Rollup 3 is on master.

[github-actions]

Thank you for your contribution! ❤️

You can try out this pull request locally by installing Rollup via

npm install rollup/rollup#prepare-browser-build

or load it into the REPL:
https://rollupjs.org/repl/?pr=4594

[codecov]

Codecov Report

Merging #4594 (3b556d6) into master (c526974) will not change coverage.
The diff coverage is n/a.

❗ Current head 3b556d6 differs from pull request most recent head 62121a5. Consider uploading reports for the commit 62121a5 to get more accurate results

@@           Coverage Diff           @@
##           master    #4594   +/-   ##
=======================================
  Coverage   98.86%   98.86%           
=======================================
  Files         209      209           
  Lines        7345     7345           
  Branches     2098     2098           
=======================================
  Hits         7262     7262           
  Misses         27       27           
  Partials       56       56           

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[lukastaegert]

This PR has been released as part of rollup@3.0.0-3. Note that this is a pre-release, so to test it, you need to install Rollup via npm install rollup@3.0.0-3 or npm install rollup@beta. It will likely become part of a regular release later.