first-interaction: Fix repository issues

Per [1], we need to use pull_request_target instead of pull_request
here. The tl;dr is that this runs as the *users* credentials, but they
may not have access to the repo.

See also [2].

[1] https://securitylab.github.com/research/github-actions-preventing-pwn-requests/
[2] actions/first-interaction#31

Signed-off-by: Kyle Mestery <[email protected]>

.github/workflows/first-interaction.yml

@@ -3,7 +3,7 @@ name: 'First Interaction'
 on:
   issues:
     types: [ opened ]
-  pull_request:
+  pull_request_target:
     branches: [ main ]
 
   workflow_dispatch: