Update workflow to test on push.

Author: jgfoster

.github/workflows/README.md

@@ -7,4 +7,4 @@ In this project, we define a workflow for each target platform.  **If you're loo
 
 The reason that all platforms are tested in _this_ project is to ensure that, as a framework, `arduino_ci` will run properly on any developer's personal workstation (regardless of OS).
 
-For testing an individual Arduino library in the context of GitHub, [Linux is the cheapest option](https://docs.github.com/en/free-pro-team@latest/github/setting-up-and-managing-billing-and-payments-on-github/about-billing-for-github-actions) and produces results identical to the other OSes.
+For testing an individual Arduino library in the context of GitHub, [Linux is the cheapest option](https://docs.github.com/en/free-pro-team@latest/github/setting-up-and-managing-billing-and-payments-on-github/about-billing-for-github-actions) and should produce results identical to the other OSes.

.github/workflows/linux.yaml

@@ -1,7 +1,7 @@
 # This is the name of the workflow, visible on GitHub UI
 name: linux
 
-on: [pull_request]
+on: [push, pull_request]
 
 jobs:
   "unittest_lint_sampleproject":

.github/workflows/macos.yaml

@@ -1,7 +1,7 @@
 # This is the name of the workflow, visible on GitHub UI
 name: macos
 
-on: [pull_request]
+on: [push, pull_request]
 
 jobs:
   "unittest_lint_sampleproject":

.github/workflows/windows.yaml

@@ -1,7 +1,7 @@
 # This is the name of the workflow, visible on GitHub UI
 name: windows
 
-on: [pull_request]
+on: [push, pull_request]
 
 jobs:
   "unittest_lint_sampleproject":