Bump bcrypt from 3.1.20 to 3.1.21 in /builder (#2912)

Bumps [bcrypt](https://github.com/bcrypt-ruby/bcrypt-ruby) from 3.1.20 to 3.1.21.
- [Release notes](https://github.com/bcrypt-ruby/bcrypt-ruby/releases)
- [Changelog](https://github.com/bcrypt-ruby/bcrypt-ruby/blob/master/CHANGELOG)
- [Commits](bcrypt-ruby/bcrypt-ruby@v3.1.20...v3.1.21)

---
updated-dependencies:
- dependency-name: bcrypt
  dependency-version: 3.1.21
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

builder/Gemfile.lock

@@ -78,7 +78,7 @@ GEM
     addressable (2.8.8)
       public_suffix (>= 2.0.2, < 8.0)
     base64 (0.3.0)
-    bcrypt (3.1.20)
+    bcrypt (3.1.21)
     bigdecimal (4.0.1)
     bootsnap (1.20.1)
       msgpack (~> 1.2)