Better fix for illegal access warnings

[melissalinkert]

61fcc36 reverts the addition of --add-opens to the default JVM options in #233. As noted in #233 (comment) and #237, that change breaks JDK 8 support.

The revert and subsequent release of 0.9.1 was the quickest way to resolve this in the short term; 0.9.1 is expected to work with JDK 8+. However, it would be still be nice to remove illegal access warnings going forward.

As @chris-allan mentioned separately, setting JDK_JAVA_OPTIONS is probably the path forward. I need a little more time to figure out how best to implement that though, and we'll want to test on a variety of platforms. @sbesson also mentioned this might be a good occasion to figure out a way to automatically test the zip; that's maybe a separate step in .github./workflows/build.yml