Fix JRuby 9.3 build

The Ruby version targeted by JRuby 9.3 is now too old for Rubygems to
run. Let's pin to the last version that works for now.

When we next have a major version bump for one of the breaking changes
we're planning to make (likely around the store interface), we'll clear
out support for any Ruby versions that have fallen out of security
support.

Signed-off-by: Chris Sinjakli <chris@sinjakli.co.uk>

Author: Sinjo

.circleci/config.yml

@@ -12,15 +12,23 @@ jobs:
 
     steps:
     - checkout
-    # JRuby <= 9.2.x is no longer supported by the `rubygems-update` gem, which now
-    # requires at least Ruby 2.6 compatibility.
+    # We need to limit the version of Rubygems that we update to for some of the older
+    # JRuby versions. Specifically:
+    #
+    #   - JRuby 9.2.x targets Ruby 2.5, and Rubygems 3.3.26 was the last version to
+    #     support that
+    #   - JRuby 9.3.x targets Ruby 2.6, and version 3.4.22 was the last version to
+    #     support that
     #
     # For now, we'll pin to the last supported version. We can drop this check once we
     # drop all those versions of JRuby.
     - run: |
-        running_old_ruby=$(ruby -e 'puts Gem::Version.new(RUBY_VERSION) < Gem::Version.new("2.6.0")')
-        if [[ "${running_old_ruby}" == "true" ]]; then 
+        running_very_old_ruby=$(ruby -e 'puts Gem::Version.new(RUBY_VERSION) < Gem::Version.new("2.6.0")')
+        running_moderately_old_ruby=$(ruby -e 'puts Gem::Version.new(RUBY_VERSION) < Gem::Version.new("3.0.0")')
+        if [[ "${running_very_old_ruby}" == "true" ]]; then
           gem update --system 3.3.26
+        elif [[ "${running_moderately_old_ruby}" == "true" ]]; then
+          gem update --system 3.4.22
         else
           gem update --system
         fi