GitHub Actions: smart run strategy (#937)

* GHA: run CI on PRs and pushes to master only

Previously, every pull request was running actions twice, since two signas were fired - push commit in the PR and new PR itself.

* Update CHANGELOG

* Review comments

Co-authored-by: Alan Crosswell <alan@columbia.edu>

Author: Rust Saiargaliev

.github/workflows/test.yml

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

AUTHORS

@@ -40,4 +40,5 @@ Tom Evans
 Dylan Giesler
 Spencer Carroll
 Dulmandakh Sukhbaatar
+Rustem Saiargaliev
 Will Beaufoy