Update gspread requirement from ==5.* to ==6.*

Updates the requirements on [gspread](https://github.com/burnash/gspread) to permit the latest version.
- [Release notes](https://github.com/burnash/gspread/releases)
- [Changelog](https://github.com/burnash/gspread/blob/master/HISTORY.rst)
- [Commits](burnash/gspread@v5.0.0...v6.0.0)

---
updated-dependencies:
- dependency-name: gspread
  dependency-type: direct:production
...

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

requirements.txt

@@ -32,7 +32,7 @@ pandera
 prometheus_pandas
 pytest-mock
 google-cloud-bigquery[pandas]==3.*
-gspread==5.*
+gspread==6.*
 
 # requests is used by deployer/commands/cilogon.py
 requests==2.*