Merge pull request swisskyrepo#815 from pgoslatara/actup/update-actions-1768915364

chore: Update outdated GitHub Actions versions

Author: swisskyrepo

.github/workflows/check-markdown.yml

@@ -5,7 +5,7 @@ jobs:
   lint:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
 

.github/workflows/mkdocs-build.yml

@@ -8,12 +8,12 @@ jobs:
   deploy:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           submodules: recursive
 
       # Checks-out submodules
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Checkout submodules
         shell: bash
         run: |