build(deps): bump rack-session from 2.0.0 to 2.1.1 in /appengine/pubsub (#1562)

Bumps [rack-session](https://github.com/rack/rack-session) from 2.0.0 to 2.1.1.
- [Release notes](https://github.com/rack/rack-session/releases)
- [Changelog](https://github.com/rack/rack-session/blob/v2.1.1/releases.md)
- [Commits](rack/rack-session@v2.0.0...v2.1.1)

---
updated-dependencies:
- dependency-name: rack-session
  dependency-version: 2.1.1
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

appengine/pubsub/Gemfile.lock

@@ -69,11 +69,12 @@ GEM
       uri
     os (1.1.4)
     public_suffix (5.0.4)
-    rack (3.0.9.1)
+    rack (3.1.15)
     rack-protection (4.0.0)
       base64 (>= 0.1.0)
       rack (>= 3.0.0, < 4)
-    rack-session (2.0.0)
+    rack-session (2.1.1)
+      base64 (>= 0.1.0)
       rack (>= 3.0.0)
     rack-test (2.1.0)
       rack (>= 1.3)