update mddiffcheck workflow with support for multiple repos (#1722)

Author: leighmcculloch

.github/workflows/mddiffcheck.yml

@@ -14,14 +14,10 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v2
       with:
-        go-version: ^1.16
-    - run: go install github.com/stellar/mddiffcheck@v1.1.0
-    - run: |
-          failed=0
-          for f in core/*.md; do
-            mddiffcheck -repo https://github.com/stellar/stellar-core "$f" || \
-            mddiffcheck -repo https://github.com/stellar/stellar-xdr "$f" || {
-              failed=1
-            }
-          done
-          exit $failed
+        go-version: ^1.24
+    - run: go install github.com/stellar/mddiffcheck@v1.2.0
+    - run: >
+        mddiffcheck
+        -repo
+        'https://github.com/stellar/stellar-core https://github.com/stellar/stellar-xdr'
+        core/*.md