ci: bump the min JRE version tested from 8 to 9

Author: flavorjones

.github/workflows/ci.yml

@@ -726,7 +726,7 @@ jobs:
       fail-fast: false
       matrix:
         jruby: ["9.4"]
-        jre: ["8", "11"]
+        jre: ["9", "11"]
     name: "jruby-${{matrix.jruby}}-jre${{matrix.jre}}-install"
     runs-on: ubuntu-latest
     steps: