Bump actions/setup-node from 5 to 6 (cylc#2340)

Bumps [actions/setup-node](https://github.com/actions/setup-node) from 5 to 6.
- [Release notes](https://github.com/actions/setup-node/releases)
- [Commits](actions/setup-node@v5...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]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/auto_publish_release.yml

@@ -27,7 +27,7 @@ jobs:
           ref: ${{ env.MERGE_SHA }}
 
       - name: Setup Node
-        uses: actions/setup-node@v5
+        uses: actions/setup-node@v6
         with:
           node-version: 'lts/*'
 

.github/workflows/main.yml

@@ -22,7 +22,7 @@ jobs:
         uses: actions/checkout@v5
 
       - name: Setup Node
-        uses: actions/setup-node@v5
+        uses: actions/setup-node@v6
         with:
           node-version: 'lts/*'
           cache: yarn
@@ -78,7 +78,7 @@ jobs:
         uses: actions/checkout@v5
 
       - name: Setup Node
-        uses: actions/setup-node@v5
+        uses: actions/setup-node@v6
         with:
           node-version: 'lts/*'
           cache: yarn

.github/workflows/renovate_validate.yml

@@ -23,7 +23,7 @@ jobs:
         uses: actions/checkout@v5
 
       - name: Setup Node
-        uses: actions/setup-node@v5
+        uses: actions/setup-node@v6
         with:
           node-version: 'lts/*'