Bump robotology/gh-action-nightly-merge from 1.3.3 to 1.4.0

Bumps [robotology/gh-action-nightly-merge](https://github.com/robotology/gh-action-nightly-merge) from 1.3.3 to 1.4.0.
- [Release notes](https://github.com/robotology/gh-action-nightly-merge/releases)
- [Commits](robotology/gh-action-nightly-merge@v1.3.3...v1.4.0)

---
updated-dependencies:
- dependency-name: robotology/gh-action-nightly-merge
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/nightly_merge.yml

@@ -15,7 +15,7 @@ jobs:
           fetch-depth: 0
 
       - name: 🔀 Merge master into maintenance
-        uses: robotology/gh-action-nightly-merge@v1.3.3
+        uses: robotology/gh-action-nightly-merge@v1.4.0
         with:
           stable_branch: "master"
           development_branch: "maintenance"
@@ -24,7 +24,7 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
       - name: 🔀 Merge staging/bugfix into maintenance
-        uses: robotology/gh-action-nightly-merge@v1.3.3
+        uses: robotology/gh-action-nightly-merge@v1.4.0
         with:
           stable_branch: "staging/bugfix"
           development_branch: "maintenance"
@@ -33,7 +33,7 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
       - name: 🔀 Merge staging/maintenance into maintenance
-        uses: robotology/gh-action-nightly-merge@v1.3.3
+        uses: robotology/gh-action-nightly-merge@v1.4.0
         with:
           stable_branch: "staging/bugfix"
           development_branch: "maintenance"
@@ -42,7 +42,7 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
       - name: 🔀 Merge maintenance into devel
-        uses: robotology/gh-action-nightly-merge@v1.3.3
+        uses: robotology/gh-action-nightly-merge@v1.4.0
         with:
           stable_branch: "maintenance"
           development_branch: "devel"