Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/nightly.yml

@@ -33,7 +33,7 @@ jobs:
       CCACHE_COMPILERCHECK: content
       CCACHE_SLOPPINESS: time_macros
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           persist-credentials: false
 

.github/workflows/stable.yml

@@ -33,7 +33,7 @@ jobs:
       CCACHE_COMPILERCHECK: content
       CCACHE_SLOPPINESS: time_macros
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           persist-credentials: false
 
@@ -125,7 +125,7 @@ jobs:
           files: |
             *.AppImage*
 
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Update LATEST_VERSION
         run: |
           echo "${{ env.VERSION }}" > ./LATEST_VERSION