ci: optimise action triggers

it is pointless to run CI jobs for pushes / PRs that only change files that
would never cause a failure, such as documentation.

this avoids wasting resources for such situations.

.github/workflows/test.yml

@@ -4,8 +4,10 @@ name: test
 on:
   push:
     branches: [master, dev]
+    paths: ['**.rs', '**.toml', '**.lock', '**.yml']
   pull_request:
     branches: [master, dev]
+    paths: ['**.rs', '**.toml', '**.lock', '**.yml']
 
 jobs:
   fmt: