Bump actions/setup-node from 4 to 6

Bumps [actions/setup-node](https://github.com/actions/setup-node) from 4 to 6.
- [Release notes](https://github.com/actions/setup-node/releases)
- [Commits](actions/setup-node@v4...v6)

---
updated-dependencies:
- dependency-name: actions/setup-node
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/build_gui.yml

@@ -52,7 +52,7 @@ jobs:
           pip install --upgrade platformio
 
       - name: Set up Node JS
-        uses: actions/setup-node@v4
+        uses: actions/setup-node@v6
         with:
           node-version: '20'
 

.github/workflows/release_validation.yaml

@@ -42,7 +42,7 @@ jobs:
           pip install --upgrade platformio
 
       - name: Set up Node JS
-        uses: actions/setup-node@v4
+        uses: actions/setup-node@v6
         with:
           node-version: '20'