Fix duplication of checks on internal PRs (#1986)

Internal PRs (that come from branches of psf/black) match both the push
and pull_request events. This leads to a duplication of test, lint, etc.
checks on such PRs. Not only is it a waste of resources, it makes the
Status Checks UI more frustrating to go through.

Patch taken from:
https://github.community/t/duplicate-checks-on-push-and-pull-request-simultaneous-event/18012

.github/workflows/doc.yml

@@ -16,8 +16,14 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    # We want to run on external PRs, but not on our own internal PRs as they'll be run
+    # by the push to the branch. Without this if check, checks are duplicated since
+    # internal PRs match both the push and pull_request events.
+    if:
+      github.event_name == 'push' || github.event.pull_request.head.repo.full_name !=
+      github.repository
 
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
 

.github/workflows/fuzz.yml

@@ -4,6 +4,13 @@ on: [push, pull_request]
 
 jobs:
   build:
+    # We want to run on external PRs, but not on our own internal PRs as they'll be run
+    # by the push to the branch. Without this if check, checks are duplicated since
+    # internal PRs match both the push and pull_request events.
+    if:
+      github.event_name == 'push' || github.event.pull_request.head.repo.full_name !=
+      github.repository
+
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false

.github/workflows/lint.yml

@@ -4,6 +4,13 @@ on: [push, pull_request]
 
 jobs:
   build:
+    # We want to run on external PRs, but not on our own internal PRs as they'll be run
+    # by the push to the branch. Without this if check, checks are duplicated since
+    # internal PRs match both the push and pull_request events.
+    if:
+      github.event_name == 'push' || github.event.pull_request.head.repo.full_name !=
+      github.repository
+
     runs-on: ubuntu-latest
     strategy:
       matrix:

.github/workflows/primer.yml

@@ -4,6 +4,13 @@ on: [push, pull_request]
 
 jobs:
   build:
+    # We want to run on external PRs, but not on our own internal PRs as they'll be run
+    # by the push to the branch. Without this if check, checks are duplicated since
+    # internal PRs match both the push and pull_request events.
+    if:
+      github.event_name == 'push' || github.event.pull_request.head.repo.full_name !=
+      github.repository
+
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false

.github/workflows/test.yml

@@ -4,6 +4,13 @@ on: [push, pull_request]
 
 jobs:
   build:
+    # We want to run on external PRs, but not on our own internal PRs as they'll be run
+    # by the push to the branch. Without this if check, checks are duplicated since
+    # internal PRs match both the push and pull_request events.
+    if:
+      github.event_name == 'push' || github.event.pull_request.head.repo.full_name !=
+      github.repository
+
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false