chore(deps): update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/.firebase/build-and-deploy.yml

@@ -32,7 +32,7 @@ jobs:
         id: remote_repo
 
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v6
         with:
           ref: ${{ github.ref }}
 

.github/workflows/build-and-deploy.yml

@@ -31,7 +31,7 @@ jobs:
         id: remote_repo
 
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v6
         with:
           ref: ${{ github.ref }}
 

.github/workflows/optimize-and-merge.yml

@@ -12,7 +12,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v6
 
       - name: Optimize with Calibre's image actions
         uses: calibreapp/image-actions@main

.github/workflows/update-views.yml

@@ -19,7 +19,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v6
         with:
           ref: master
           fetch-depth: 0