CI: Run shellcheck for test scripts

.github/workflows/ruby.yml

@@ -25,6 +25,9 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
+    - name: Shellcheck
+      if: matrix.os == 'ubuntu-latest'
+      run: shellcheck test/run test/checks
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:

test/run

@@ -103,4 +103,5 @@ function summary() {
 
 trap summary EXIT
 
+# shellcheck source=test/checks
 source "$(dirname "${BASH_SOURCE[0]}")/checks"