Bump withastro/action from 3 to 4

Bumps [withastro/action](https://github.com/withastro/action) from 3 to 4.
- [Release notes](https://github.com/withastro/action/releases)
- [Commits](withastro/action@v3...v4)

---
updated-dependencies:
- dependency-name: withastro/action
  dependency-version: '4'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/build.yml

@@ -20,7 +20,7 @@ jobs:
       - name: ⬇️ Checkout
         uses: actions/checkout@v4
       - name: Install, build, and upload your site
-        uses: withastro/action@v3
+        uses: withastro/action@v4
 
   deploy:
     needs: build