Ease pre-pull request fork CI as well as github-actions based dispatch (#229)

.github/workflows/action.yml

@@ -1,13 +1,7 @@
 ---
 name: action
 
-on:
-  push:
-    branches:
-      - main
-  pull_request:
-    branches:
-      - main
+on: [push, workflow_dispatch]
 
 env:
   GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}

.github/workflows/hexpm-mirrors.yml

@@ -1,13 +1,7 @@
 ---
 name: hexpm-mirrors
 
-on:
-  push:
-    branches:
-      - main
-  pull_request:
-    branches:
-      - main
+on: [push, workflow_dispatch]
 
 jobs:
   test-failing-first-mirror:

.github/workflows/ubuntu.yml

@@ -1,13 +1,7 @@
 ---
 name: ubuntu
 
-on:
-  push:
-    branches:
-      - main
-  pull_request:
-    branches:
-      - main
+on: [push, workflow_dispatch]
 
 jobs:
   integration_test:

.github/workflows/windows.yml

@@ -1,13 +1,7 @@
 ---
 name: windows
 
-on:
-  push:
-    branches:
-      - main
-  pull_request:
-    branches:
-      - main
+on: [push, workflow_dispatch]
 
 jobs:
   integration_test: