ruby/spec minimum Ruby version is 2.6 now

Author: eregon

.github/workflows/ci.yml

@@ -192,7 +192,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [2.5, 2.6, 2.7]
+        ruby: [2.6, 2.7, 3.0]
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2

ci.jsonnet

@@ -311,7 +311,7 @@ local part_definitions = {
         "CHECK_LEAKS": "true",
       },
       run+: jt(["-u", mri_path(mri_version), "mspec", "spec/ruby"]) +
-            jt(["-u", mri_path("2.5.7"), "mspec", "spec/ruby"]),
+            jt(["-u", mri_path("2.6.6"), "mspec", "spec/ruby"]),
     },
 
     test_fast: {