chore: Check commit messages as GitHub action

- Since Standard Version isn't able to correctly identify what the new
  version of a package should be when the commit message begins with an
  unknown type, this new GitHub action will cause PRs to have a failing
  build when any commit contains an unsupported commit type.

.github/workflows/check-commit-messages.yml

@@ -0,0 +1,27 @@
+name: 'Check Commit Message'
+
+on:
+  pull_request:
+    types:
+      - opened
+      - edited
+      - reopened
+      - synchronize
+  push:
+    branches:
+      - master
+
+jobs:
+  check-commit-message:
+    name: Check Commit Message
+    runs-on: ubuntu-latest
+    steps:
+      - name: Commit begins with supported commit type
+        uses: gsactions/commit-message-checker@v1
+        with:
+          pattern: '^(feat|fix|docs|style|refactor|test|chore).+'
+          error: 'Commit messages must begin with a valid commit type. See "Commit Style" under CONTRIBUTING.md for more details.'
+          excludeDescription: 'true'
+          excludeTitle: 'true'
+          checkAllCommitMessages: 'true'
+          accessToken: ${{ secrets.GITHUB_TOKEN }}

CONTRIBUTING.md

@@ -10,13 +10,26 @@
 - Assign a [sparkboxer][contributors] to review your PR
 
 ## Commit Style
-We use [Conventional Commits] and [Standard Version] to automate versioning of this package. Commit messages must be prefixed with a valid commit type.
+We use [Conventional Commits] and [Standard Version] to automate versioning of this package. Commit messages must be prefixed with a valid commit type and the commit type cannot be prefixed with any additional text.
+
+Supported commit types include `feat`, `fix`, `docs`, `style`, `refactor`, and `test`.
+
+Valid example:
 
-Example:
 ```sh
 feat: add new linting rule for ...
 ```
 
+Invalid examples:
+
+```sh
+ feature: add new linting rule for ...
+ ```
+
+ ```sh
+ :sparkles: feat: add new linting rule for ...
+ ```
+
 ℹ️ See the [Conventional Commits] page for further details on available commit types and how to handle breaking changes.
 
 ## Creating a Release