Add brakeman as a development dependency in playbook (#4121)

**What does this PR do?**

Adds brakeman as a development dependency. This allows the scanner to
work correctly, and developers to scan locally. It does not affect
production code.


**How to test?** Steps to confirm the desired behavior:

This does not contain any functional changes. If you want to run
brakeman locally, make sure you're inside of playbook/playbook and have
bundled. Then run `brakeman scan .`


#### Checklist:
- [ ] **LABELS** Add a label: `enhancement`, `bug`, `improvement`, `new
kit`, `deprecated`, or `breaking`. See [Changelog &
Labels](https://github.com/powerhome/playbook/wiki/Changelog-&-Labels)
for details.
- [ ] **DEPLOY** I have added the `milano` label to show I'm ready for a
review.
- [ ] **TESTS** I have added test coverage to my code.

Author: that-jill

Diff for: playbook/Gemfile.lock

@@ -84,6 +84,8 @@ GEM
     babel-transpiler (0.7.0)
       babel-source (>= 4.0, < 6)
       execjs (~> 2.0)
+    brakeman (7.0.0)
+      racc
     builder (3.2.4)
     byebug (11.1.3)
     concurrent-ruby (1.2.3)
@@ -296,6 +298,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
+  brakeman (= 7.0.0)
   byebug (>= 11.0.0)
   github_changelog_generator (= 1.15.2)
   playbook_ui!

Diff for: playbook/playbook_ui.gemspec

@@ -40,6 +40,7 @@ Gem::Specification.new do |s|
   s.add_dependency "view_component", "2.83.0"
   s.add_dependency "webpacker-react", "~> 0.3.2"
 
+  s.add_development_dependency "brakeman", "7.0.0"
   s.add_development_dependency "byebug", ">= 11.0.0"
   s.add_development_dependency "github_changelog_generator", "1.15.2"
   s.add_development_dependency "rails", ">= 5.2.4.5"