workflows: install svn when brew fetch needs it

.github/workflows/scheduled.yml

@@ -149,7 +149,19 @@ jobs:
       - name: Check formula for missing sources.
         id: fetch
         if: always() && steps.archived.conclusion != 'failure'
-        run: brew fetch --build-from-source "$FORMULA"
+        run: |
+          FETCH_OUTPUT=$(brew fetch --build-from-source "$FORMULA" 2>&1 || true)
+          FETCH_EXIT_CODE=$?
+          echo "$FETCH_OUTPUT"
+
+          if echo "$FETCH_OUTPUT" | grep -q "You must: brew install svn"; then
+            echo "SVN required. Installing..."
+            brew install svn
+            echo "Retrying fetch..."
+            brew fetch --build-from-source "$FORMULA"
+          elif [ $FETCH_EXIT_CODE -ne 0 ]; then
+            exit $FETCH_EXIT_CODE
+          fi
 
       - name: Report fetch issues
         if: failure() && steps.fetch.conclusion == 'failure'