add workflow dispatches to some of the tests

Author: chrishavlin

.github/workflows/check-build.yml

@@ -1,5 +1,7 @@
 name: Check Build
-on: pull_request
+on: 
+  pull_request:
+  workflow_dispatch:
 
 jobs:
   twinecheck:

.github/workflows/check-manifest.yml

@@ -1,6 +1,7 @@
 name: check MANIFEST.in
 on:
-  pull_request
+  pull_request:
+  workflow_dispatch:
 
 jobs:
   check-manifest:

.github/workflows/run-pytest-tests.yml

@@ -1,6 +1,8 @@
 name: Run tests
 
-on: [pull_request]
+on: 
+  pull_request:
+  workflow_dispatch:
 
 jobs:
   test: