Change PR workflow to pull_request_target

This should allow secrets to be used in PRs
diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml
index aef7147..e93e9cd 100644
--- a/.github/workflows/validate.yml
+++ b/.github/workflows/validate.yml
@@ -1,7 +1,7 @@
 name: Validate
 
 on:
-  pull_request:
+  pull_request_target:
   push:
     branches:
       - master