[action] Only include merge message on sdk changes (#6955)

The "Merge to main" workflow adds a comment to the PR so authors know
that their changes shouldn't break the main branch, as it should always
remain stable and releasable. This only makes sense when the change
affects an SDK, as only those get released. Now we filter the message so
it doesn't spam PRs that only touch infra (plugin & github folders)

Author: rlazo

.github/workflows/merge-to-main.yml

@@ -6,16 +6,45 @@ on:
       - main
     types:
       - opened
-      - labeled
-      - unlabeled
+      - synchronize
 
 jobs:
   pr-message:
     runs-on: ubuntu-latest
     permissions:
       pull-requests: write
     steps:
-    - uses: mshick/add-pr-comment@b8f338c590a895d50bcbfa6c5859251edc8952fc # v2.8.2
+    - name: Checkout repo
+      uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      with:
+        fetch-depth: 0
+        submodules: false
+
+    - name: Filter paths
+      id: filter
+      run: |
+        MERGE_BASE=$(git merge-base origin/${GITHUB_BASE_REF} origin/${GITHUB_HEAD_REF})
+        FILES=$(git diff --name-only $MERGE_BASE origin/${GITHUB_HEAD_REF})
+        IGNORE=true
+        for FILE in $FILES; do
+          if [[ $FILE != plugins/* && $FILE != .github/* ]]; then
+            IGNORE=false
+            break
+          fi
+        done
+
+        if $IGNORE; then
+          echo "ignore=true" >> $GITHUB_OUTPUT
+          echo "Filter result code: ignore = true"
+        else
+          echo "ignore=false" >> $GITHUB_OUTPUT
+          echo "Filter result code: ignore = false"
+        fi
+      shell: bash
+
+    - name: Add PR comment
+      if: steps.filter.outputs.ignore == 'false'
+      uses: mshick/add-pr-comment@b8f338c590a895d50bcbfa6c5859251edc8952fc # v2.8.2
       with:
         message: >
           ### 📝 PRs merging into main branch
@@ -27,4 +56,5 @@ jobs:
           branch when the code complete and ready to be released.
 
     - name: Success
+      if: steps.filter.outputs.ignore == 'false'
       run: exit 0