ci: Allow explicitly triggering CI runs

Author: sdroege

.github/workflows/CI.yml

@@ -2,6 +2,7 @@ on:
   push:
     branches: [master]
   pull_request:
+  workflow_dispatch:
 
 name: CI
 

.github/workflows/docs.yml

@@ -2,6 +2,7 @@ on:
   push:
     branches: [master]
   pull_request:
+  workflow_dispatch:
   release:
     types: [published]
 

.github/workflows/windows.yml

@@ -2,6 +2,7 @@ on:
   push:
     branches: [master]
   pull_request:
+  workflow_dispatch:
 
 name: Windows