authentication to private package feed failing on jruby-head

[baywet]

Environment Information

Provide at least:

• JRuby version (jruby -v) and command line (flags, JRUBY_OPTS, etc) jruby 9.4.0.0-SNAPSHOT (3.1.0) 2022-02-08 3562498 OpenJDK 64-Bit Server VM 11.0.14+9 on 11.0.14+9 +jit [linux-x86_64]
• Operating system and platform (e.g. uname -a) ubuntu agent for GitHub actions

Other relevant info you may wish to add:

• Installed or activated gems
• Application/framework version (e.g. Rails, Sinatra) none
• Environment variables BUNDLE_HTTPS://RUBYGEMS__PKG__GITHUB__COM/MICROSOFT/: "${{ secrets.PUBLISH_GH_USERNAME }}:${{ secrets.PUBLISH_GH_TOKEN }}"

Expected Behavior
bundle install to complete successfully with a private feed (GitHub packages)

Actual Behavior

install fails with the following error message even though the environment variable is set and the same workflow is working with 2.[5-7], 3.0, latest, head, jruby, truffleruby, truffleruby-head. It also used to be working fine on jruby-head until this version included.
jruby 9.4.0.0-SNAPSHOT (3.1.0) 2022-01-25 abadd2f OpenJDK 64-Bit Server VM 25.322-b06 on 1.8.0_322-b06 +jit [darwin-x86_64]

Authentication is required for rubygems.pkg.github.com.
  Please supply credentials for this source. You can do this by running:
  `bundle config set --global rubygems.pkg.github.com username:password`
  or by storing the credentials in the `BUNDLE_RUBYGEMS__PKG__GITHUB__COM`
  environment variable

You can see the workflow definition here (hasn't changed in 3 months). A failed execution here, and a successful one here