Bump fortran-lang/setup-fpm from 5 to 6

Bumps [fortran-lang/setup-fpm](https://github.com/fortran-lang/setup-fpm) from 5 to 6.
- [Release notes](https://github.com/fortran-lang/setup-fpm/releases)
- [Commits](fortran-lang/setup-fpm@v5...v6)

---
updated-dependencies:
- dependency-name: fortran-lang/setup-fpm
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/ci.yml

@@ -34,7 +34,7 @@ jobs:
       - name: macos workaround
         if: runner.os == 'macos'
         run: brew install gcc@10
-      - uses: fortran-lang/setup-fpm@v5
+      - uses: fortran-lang/setup-fpm@v6
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
       - run: fpm test