ci: Bump actions/checkout from 6 to 7

Bumps [actions/checkout](https://github.com/actions/checkout) from 6 to 7.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v6...v7)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/e2e.yml

@@ -13,7 +13,7 @@ jobs:
     timeout-minutes: 20
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
 
       - name: Set up Node.js
         uses: actions/setup-node@v6

.github/workflows/frontend.yml

@@ -21,7 +21,7 @@ jobs:
         working-directory: frontend
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
 
       - name: Set up Node.js
         uses: actions/setup-node@v6

.github/workflows/tests.yml

@@ -33,7 +33,7 @@ jobs:
         working-directory: backend
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
 
       - name: Set up Python 3.11
         uses: actions/setup-python@v6