Add Standard workflow

This commit adds a GitHub Action that does Standard linting and
formatting checks.

Ref:
- https://github.com/standardrb/standard-ruby-action

.github/workflows/standardrb.yml

@@ -0,0 +1,22 @@
+---
+name: Lint with StandardRB
+
+on: [push]
+
+jobs:
+ build:
+ runs-on: ubuntu-latest
+
+ permissions:
+ contents: read
+ checks: write
+
+ steps:
+ - uses: actions/checkout@v4
+ - name: StandardRB Linter
+ uses: testdouble/[email protected]
+ env:
+ GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+ with:
+ ruby-version: "3.3.5"
+ autofix: false