allow workflows to be triggered manually

.github/workflows/docker.yml

@@ -1,6 +1,7 @@
 name: docker
 
 on:
+  workflow_dispatch:
   push:
     tags:
     - v[0-9]+.[0-9]+.[0-9]+

.github/workflows/executables.yml

@@ -1,6 +1,10 @@
 name: executables
 
-on: [push]
+on:
+  workflow_dispatch:
+  push:
+    branches:
+    - master
 
 jobs:
   build:

.github/workflows/tests.yml

@@ -1,6 +1,7 @@
 name: tests
 
 on:
+  workflow_dispatch:
   push:
     branches:
     - master