build(deps): bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v4...v6)

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

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/build-quickgui.yml

@@ -27,7 +27,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: "Checkout 🥡"
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: "Install Flutter 🦋"
         uses: subosito/flutter-action@v2
         with:
@@ -56,7 +56,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: "Checkout 🥡"
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: "Install Flutter 🦋"
         uses: subosito/flutter-action@v2
         with:
@@ -118,7 +118,7 @@ jobs:
       contents: "read"
     steps:
       - name: "Checkout 🥡"
-        uses: "actions/checkout@v4"
+        uses: "actions/checkout@v6"
       - name: "Install Nix ❄️"
         uses: "DeterminateSystems/nix-installer-action@v22"
       - name: "Enable Magic Nix Cache 🪄"

.github/workflows/flake-checker.yml

@@ -13,7 +13,7 @@ jobs:
     name: Flake Checker
     runs-on: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - uses: DeterminateSystems/nix-installer-action@v22

.github/workflows/flake-updater.yml

@@ -10,7 +10,7 @@ jobs:
     name: Flake Lock Updater
     runs-on: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - uses: DeterminateSystems/nix-installer-action@v22

.github/workflows/publish-quickgui.yml

@@ -24,7 +24,7 @@ jobs:
     name: "Check versions ⚖️"
     runs-on: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - name: "Compare App and Git versions 🟰"
@@ -46,7 +46,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: "Checkout 🥡"
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: "Install Flutter 🦋"
         uses: subosito/flutter-action@v2
         with:
@@ -100,7 +100,7 @@ jobs:
       id-token: "write"
       contents: "read"
     steps:
-      - uses: "actions/checkout@v4"
+      - uses: "actions/checkout@v6"
         with:
           ref: "${{ (inputs.tag != null) && format('refs/tags/{0}', inputs.tag) || '' }}"
       - uses: "DeterminateSystems/nix-installer-action@v22"
@@ -117,7 +117,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: "Checkout 🥡"
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: "Install Flutter 🦋"
         uses: subosito/flutter-action@v2
         with: