Unify CI for pull requests and pushes to main (#50)

This patch brings together the GitHub workflows for pull requests and
pushes to main so that there is a single workflow for continuous
integration.

The reason why they were separated was a misconception on my side how
GitHub filters the events.

.github/workflows/test-on-pull-request.yml → .github/workflows/ci.yml

@@ -1,6 +1,11 @@
-name: Test-on-pull-request
-
-on: [pull_request]
+name: CI
+
+on:
+  push:
+    branches: [ master, main ]
+    tags: [ "**" ]
+  pull_request:
+    branches: [ "**" ]
 
 jobs:
   Execute:

README.rst

@@ -1,9 +1,9 @@
 icontract-hypothesis
 ====================
 
-.. image:: https://github.com/mristin/icontract-hypothesis/workflows/Test-on-push-to-main/badge.svg
-    :target: https://github.com/mristin/icontract-hypothesis/actions?query=workflow%3ATest-on-push-to-main
-    :alt: Test
+.. image:: https://github.com/mristin/icontract-hypothesis/workflows/CI/badge.svg
+    :target: https://github.com/mristin/icontract-hypothesis/actions?query=workflow%3ACI
+    :alt: Continuous integration
 
 .. image:: https://coveralls.io/repos/github/mristin/icontract-hypothesis/badge.svg?branch=main
     :target: https://coveralls.io/github/mristin/icontract-hypothesis?branch=main