ci: migrate runs-on to Twilio runner labels

Repoints runs-on to the standard Twilio runner labels for this repo.
Unmapped runners (macOS, matrix expressions, etc.) left as-is.

Author: charlottestjohn

.github/workflows/delete-old-branches.yml

@@ -7,7 +7,7 @@ on:
 jobs:
   delete-old-branches:
     name: Delete old branches
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-latest-large
     steps:
       - name: Checkout repository
         uses: actions/checkout@v2

.github/workflows/maven.yml

@@ -10,7 +10,7 @@ on:
 jobs:
   publish:
     name: Publish to Maven Central
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-latest-large
     permissions:
       contents: read