Add workflow dispatch to test github workflow

Author: ericpre

.github/workflows/tests.yml

@@ -14,6 +14,8 @@ on:
   schedule:
     # 3:47 UTC on Saturdays
     - cron: "47 3 * * 6"
+  workflow_dispatch:
+    workflow: "*"
 
 env:
   NO_AT_BRIDGE: 1  # Necessary for GTK3 interactive test.
@@ -22,7 +24,7 @@ env:
 
 jobs:
   test:
-    if: "github.repository == 'matplotlib/matplotlib' && !contains(github.event.head_commit.message, '[ci skip]') && !contains(github.event.head_commit.message, '[skip ci]') && !contains(github.event.head_commit.message, '[skip github]')"
+    if: "github.event_name == 'workflow_dispatch' || github.repository == 'matplotlib/matplotlib' && !contains(github.event.head_commit.message, '[ci skip]') && !contains(github.event.head_commit.message, '[skip ci]') && !contains(github.event.head_commit.message, '[skip github]')"
     name: "Python ${{ matrix.python-version }} on ${{ matrix.os }} ${{ matrix.name-suffix }}"
     runs-on: ${{ matrix.os }}