CI: add julia-format action

fixes #169

Author: alyst

.JuliaFormatter.toml

@@ -0,0 +1,13 @@
+name: Format suggestions
+on:
+  pull_request:
+    # this argument is not required if you don't use the `suggestion-label` input
+    types: [ opened, reopened, synchronize, labeled, unlabeled ]
+jobs:
+  code-style:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: julia-actions/julia-format@v2
+      with:
+        julia-version: '1'
+        suggestion-label: 'format suggestion'