Add CI check to forbid filenames with capital letters in them (#3807)

.github/workflows/lint.yml

@@ -23,6 +23,19 @@ jobs:
       - name: Checkout repo
         uses: actions/checkout@a12a3943b4bdde767164f792f33f40b04645d846  # v3.0.0
 
+      - name: Lint filenames (no capital characters)
+        run: |
+          find . -type f -name "*[[:upper:]]*" \
+            ! -path "./node_modules/*" \
+            ! -path "./coverage/*" \
+            ! -path "*/dist/*" \
+            ! -path "*/build/*" \
+            ! -path "*/target/*" \
+            ! -path "./.git/*" \
+            ! -path "*/.DS_Store" \
+            > tmp.txt
+          diff <(sort .github/whitelist-capital-letters.txt) <(sort tmp.txt)
+
       - name: Set up Node
         uses: actions/setup-node@9ced9a43a244f3ac94f13bfd896db8c8f30da67a  # v3.0.0
         with: