Run GH Actions on separate events (push, pull_request). (#88)

* Run GH Actions on separate events (push, pull_request).

It should help to avoid duplicate execution in the pull requests.

* Update remaining GH workflows

.github/workflows/staticcheck.yml

@@ -1,6 +1,12 @@
 name: Static Checks
 
-on: [ "push", "pull_request" ]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
 
 jobs:
   staticcheck:

.github/workflows/tests.yml

@@ -1,6 +1,12 @@
 name: Go tests
 
-on: [ push, pull_request ]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
 
 jobs:
   go-test:

.github/workflows/vet.yml

@@ -1,6 +1,12 @@
 name: Linter
 
-on: [ "push", "pull_request" ]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
 
 jobs:
   vet: