ci(actions): remove trigger on pull request

Author: amyheather

.github/workflows/R-CMD-check.yaml

@@ -2,8 +2,7 @@
 # Need help debugging build failures? Start at https://github.com/r-lib/actions#where-to-find-help
 on:
   push:
-    branches: [main, master]
-  pull_request:
+    branches: [main]
   workflow_dispatch:
 
 name: R-CMD-check.yaml

.github/workflows/lint.yaml

@@ -4,7 +4,6 @@
 on:
   push:
     branches: [main]
-  pull_request:
   workflow_dispatch:
 
 name: lint