Fix Markdown Lint (#25)

The linter was not checking any files.

.github/workflows/markdown-lint.yml

@@ -1,6 +1,7 @@
 name: markdown-linting
 
 on:
+
   push:
     branches: 
       - '**'
@@ -13,10 +14,19 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
-        with:
-          ref: ${{ github.event.pull_request.base.ref }}
+        uses: actions/checkout@v2
+
+      - name: Get changed files
+        continue-on-error: true
+        run: |
+          echo "CHANGED_FILES<<EOF" >> $GITHUB_ENV
+          gh pr diff ${{ github.event.number }} --name-only | sed -e 's|$|,|' | xargs -i echo "{}" >> $GITHUB_ENV
+          echo "EOF" >> $GITHUB_ENV
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+
       - name: Markdown Linter
         uses: DavidAnson/markdownlint-cli2-action@v15
         with:
-          globs: '/*.md'
+          globs: ${{ env.CHANGED_FILES }}