Build(deps): bump gds-sso from 21.0.0 to 21.1.0

Bumps [gds-sso](https://github.com/alphagov/gds-sso) from 21.0.0 to 21.1.0.
- [Changelog](https://github.com/alphagov/gds-sso/blob/main/CHANGELOG.md)
- [Commits](alphagov/gds-sso@v21.0.0...v21.1.0)

---
updated-dependencies:
- dependency-name: gds-sso
  dependency-version: 21.1.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

Gemfile.lock

@@ -145,7 +145,7 @@ GEM
       plek (>= 1.9.0)
       rack (>= 2.2.0)
       rest-client (~> 2.0)
-    gds-sso (21.0.0)
+    gds-sso (21.1.0)
       oauth2 (~> 2.0)
       omniauth (~> 2.1)
       omniauth-oauth2 (~> 1.8)