Drop JRuby 9.3 CI

It appears to have keyword argument issues that do not affect
JRuby 9.1, 9.2, or 9.4.

Author: jeremyevans

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest]
-        ruby: [ "2.0.0", 2.1, 2.3, 2.4, 2.5, 2.6, 2.7, "3.0", 3.1, 3.2, 3.3, 3.4, jruby-9.3, jruby-9.4 ]
+        ruby: [ "2.0.0", 2.1, 2.3, 2.4, 2.5, 2.6, 2.7, "3.0", 3.1, 3.2, 3.3, 3.4, jruby-9.4 ]
         include:
           - { os: ubuntu-22.04, ruby: "1.9.3" }
           - { os: ubuntu-22.04, ruby: jruby-9.1 }