ci: update workflow dispatch

infection.yml used workflow_call

I don't think I've seen that in a while and it should be workflow_dispatch if I remember rightly.

.github/workflows/infection.yml

@@ -1,6 +1,6 @@
 name: Mutation tests
 on:
-  workflow_call:
+  workflow_dispatch:
 jobs:
   mutation_testing:
     runs-on: ubuntu-latest