[INFRA] Only run GH WF on source code changes (#62)

Avoid building when documentation is updated.

Author: tbouffard

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

@@ -5,9 +5,25 @@ on:
   push:
     branches:
       - main
+    paths:
+      - '.github/workflows/R-CMD-check.yaml'
+      - 'R/**/*'
+      - 'inst/**/*'
+      - 'man/**/*'
+      - '.Rbuildignore'
+      - 'DESCRIPTION'
+      - 'NAMESPACE'
   pull_request:
     branches:
       - main
+    paths:
+      - '.github/workflows/R-CMD-check.yaml'
+      - 'R/**/*'
+      - 'inst/**/*'
+      - 'man/**/*'
+      - '.Rbuildignore'
+      - 'DESCRIPTION'
+      - 'NAMESPACE'
 
 name: R-CMD-check