chore: add workflow_dispatch to security-code-scanner (#131)

## Summary 

This pull request updates the Security Code Scanner by adding the
`workflow_dispatch` trigger. This trigger allows for the Code Scanner to
be manually triggered from your repository's `Action` tab.


For further questions, please contact the MetaMask Security team.

Author: metamaskbot

.github/workflows/security-code-scanner.yml

@@ -1,10 +1,13 @@
-name: 'MetaMask Security Code Scanner'
+name: MetaMask Security Code Scanner
 
 on:
   push:
-    branches: ['main']
+    branches:
+      - main
   pull_request:
-    branches: ['main']
+    branches:
+      - main
+  workflow_dispatch:
 
 jobs:
   run-security-scan: