ci: use a compatible bundler version with older ruby

Rubygems 3.3.22 is the minimum needed to correctly detect and use
`-linux-musl` and `-linux-gnu` native gems.

rake-compiler/rake-compiler#236 introduced a
minimum rubygems version for these native platform gems to provide a
sensible error message.

.github/workflows/ci.yml

@@ -362,4 +362,6 @@ jobs:
           name: cruby-x86_64-linux-musl-gem
           path: gems
       - run: apk add build-base
+      - if: matrix.ruby == '3.0' # https://github.com/rake-compiler/rake-compiler/pull/236
+        run: gem install bundler
       - run: ./bin/test-gem-install ./gems