Set shell: bash by default on all workflows

.github/workflows/__rubocop-multi-language.yml

@@ -24,6 +24,9 @@ on:
     inputs: {}
   workflow_call:
     inputs: {}
+defaults:
+  run:
+    shell: bash
 jobs:
   rubocop-multi-language:
     strategy:
@@ -53,13 +56,10 @@ jobs:
         with:
           ruby-version: 2.6
       - name: Install Code Scanning integration
-        shell: bash
         run: bundle add code-scanning-rubocop --version 0.3.0 --skip-install
       - name: Install dependencies
-        shell: bash
         run: bundle install
       - name: RuboCop run
-        shell: bash
         run: |
           bash -c "
             bundle exec rubocop --require code_scanning --format CodeScanning::SarifFormatter -o rubocop.sarif