Drop CI support of ruby 2.5

Chef 17 requires at least 2.6

Signed-off-by: Baptiste Courtois <[email protected]>

Author: Annih

.github/workflows/ci.yml

@@ -5,7 +5,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby-version: ['2.5', '2.7']
+        ruby-version: ['2.7']
     steps:
     - uses: actions/checkout@v2
     - uses: ruby/setup-ruby@v1