Build: Bump gcsfs from 2026.6.0 to 2026.8.1 (#4053)

Bumps [gcsfs](https://github.com/fsspec/gcsfs) from 2026.6.0 to 2026.8.1.
- [Release notes](https://github.com/fsspec/gcsfs/releases)
- [Commits](fsspec/gcsfs@2026.6.0...2026.8.1)

---
updated-dependencies:
- dependency-name: gcsfs
  dependency-version: 2026.8.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]