ci: Replace pull_request with pull_request_target

This makes the coverage token available in forks.

.github/workflows/ci.yaml

@@ -1,6 +1,6 @@
 name: Test
 on:
-  pull_request:
+  pull_request_target:
   push:
     branches:
       - master

.github/workflows/lint.yml

@@ -1,7 +1,7 @@
 name: Lint check
 run-name: Lint code
 on:
-  pull_request:
+  pull_request_target:
   push:
     branches:
       - master