Bump actions/checkout from 2 to 4 (#46)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v4)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/bump-staging.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout current repository
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Get latest commit SHA and date from pathoplexus/pathoplexus
         id: get_commit_info

.github/workflows/promote-staging-to-production.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout current repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Get staging SHA
         id: get_staging_sha

.github/workflows/self-approval-check.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Check if PR from GitHub Actions is self-approved
         id: check-self-approval

.github/workflows/use-prod-sha-for-demo.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Get production SHA
         id: get_production_sha