Add Spellcheck GitHub Action

This is setup to display typos in a PR review UI and will warn (but not error) if any detected.

.github/workflows/spellcheck.yml

@@ -0,0 +1,20 @@
+name: 'Check spelling'
+on: # rebuild any PRs and main branch changes
+  push:
+    branches-ignore:
+      - "dependabot/**"
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  spellcheck:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: streetsidesoftware/cspell-action@v2
+        with:
+          inline: warning
+          strict: false
+          incremental_files_only: true