Merge pull request #940 from y-yagi/fix_ruby24_build

Use Ubuntu 22.04 image to fix broken Ruby 2.4 build

Author: y-yagi

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
     name: >-
       rspec (${{ matrix.ruby }})
 
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
 
     strategy:
       fail-fast: false