Pin standard ruby_version to 3.1

At 3.2, standardrb begins enforcing use of anonymous positional
arguments forwarding, which breaks the code for any older Ruby
versions, such as 2.5 to 3.1 in our CI test matrix.

.github/workflows/push.yml

@@ -58,7 +58,10 @@ jobs:
       - uses: ruby/setup-ruby@v1
         with:
           bundler-cache: true
-          ruby-version: "3.3"
+          # Setting this later than 3.1 requires use of anonymous positional
+          #  arguments forwarding, which breaks all versions earlier than 3.2
+          #  in our test matrix
+          ruby-version: "3.1"
       - name: Install dependencies
         run: bundle install
       - name: Run the tests

.standard.yml

@@ -0,0 +1 @@
+ruby_version: 3.1