ci: point workflow triggers at main instead of master

.github/workflows/ci.yml

@@ -3,7 +3,7 @@ name: CI
 on:
   # PR branches only, as in the org's other repos.
   push:
-    branches-ignore: [master]
+    branches-ignore: [main]
   workflow_dispatch:
 
 concurrency:

.github/workflows/release-please.yml

@@ -2,7 +2,7 @@ name: Release Please
 
 on:
   push:
-    branches: [master]
+    branches: [main]
 
 permissions:
   contents: write

.github/workflows/security.yml

@@ -3,7 +3,7 @@ name: Security
 # Image scan. Separate from CI so a finding can't block auto-merge of an unrelated Dependabot fix.
 on:
   pull_request:
-    branches: [master]
+    branches: [main]
   schedule:
     - cron: '0 6 * * 1'
   workflow_dispatch: