ci: run github actions on pull requests

Closes getodk#1315

.github/workflows/oidc-e2e.yml

@@ -1,6 +1,8 @@
 name: OIDC e2e tests
 
-on: push
+on:
+  push:
+  pull_request:
 
 env:
   DEBUG: pw:api

.github/workflows/oidc-integration.yml

@@ -1,6 +1,8 @@
 name: OIDC integration tests
 
-on: push
+on:
+  push:
+  pull_request:
 
 jobs:
   oidc-integration-test:

.github/workflows/s3-e2e.yml

@@ -1,6 +1,8 @@
 name: S3 E2E Tests
 
-on: push
+on:
+  push:
+  pull_request:
 
 jobs:
   s3-e2e:

.github/workflows/standard-e2e.yml

@@ -1,6 +1,8 @@
 name: Standard E2E Tests
 
-on: push
+on:
+  push:
+  pull_request:
 
 env:
   LOG_LEVEL: DEBUG

.github/workflows/standard-suite.yml

@@ -1,6 +1,8 @@
 name: Full Standard Test Suite
 
-on: push
+on:
+  push:
+  pull_request:
 
 jobs:
   standard-tests: