(maint) Standardizes Rubies in GitHub Actions

The Ruby versions used in our GitHub Actions were inconsistent.
This commit sets all Ruby versions to use the short version (e.g.
2.5 instead of 2.5.9) for all Rubies to automatically match the
latest release of that version.

Author: mhashizume

.github/workflows/task_acceptance_tests.yaml

@@ -15,7 +15,7 @@ jobs:
         os: [ 'centos-7', 'ubuntu-18.04', 'rocky-8' ]
 
     env:
-      ruby_version: 2.5.9
+      ruby_version: 2.5
       GEM_BOLT: true
       BEAKER_debug: true
       BEAKER_set: docker/${{ matrix.os }}

.github/workflows/unit_tests_with_nightly_puppet_gem.yaml

@@ -16,7 +16,7 @@ jobs:
         puppet_version: [ 6, 7 ]
         include:
           - puppet_version: 6
-            ruby: 2.5.8
+            ruby: 2.5
           - puppet_version: 7
             ruby: 2.7
 

.github/workflows/unit_tests_with_released_puppet_gem.yaml

@@ -16,7 +16,7 @@ jobs:
         puppet_version: [ 6, 7 ]
         include:
           - puppet_version: 6
-            ruby: 2.5.8
+            ruby: 2.5
           - puppet_version: 7
             ruby: 2.7