Add PR template and auto-close PR on subtree split repositories

Author: GromNaN

.gitattributes

@@ -1,4 +1,3 @@
 /Tests export-ignore
 /phpunit.xml.dist export-ignore
-/.gitattributes export-ignore
-/.gitignore export-ignore
+/.git* export-ignore

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,8 @@
+Please do not submit any Pull Requests here. They will be closed.
+---
+
+Please submit your PR here instead:
+https://github.com/symfony/symfony
+
+This repository is what we call a "subtree split": a read-only subset of that main repository.
+We're looking forward to your PR there!

.github/workflows/close-pull-request.yml

@@ -0,0 +1,20 @@
+name: Close Pull Request
+
+on:
+ pull_request_target:
+ types: [opened]
+
+jobs:
+ run:
+ runs-on: ubuntu-latest
+ steps:
+ - uses: superbrothers/close-pull-request@v3
+ with:
+ comment: |
+ Thanks for your Pull Request! We love contributions.
+
+ However, you should instead open your PR on the main repository:
+ https://github.com/symfony/symfony
+
+ This repository is what we call a "subtree split": a read-only subset of that main repository.
+ We're looking forward to your PR there!