MNT Replace travis with github actions CI

.github/workflows/ci.yml

@@ -0,0 +1,16 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+  # Every Monday at 2:20pm UTC
+  schedule:
+    - cron: '20 14 * * 1'
+
+jobs:
+  ci:
+    name: CI
+    # Only run cron on the silverstripe account
+    if: (github.event_name == 'schedule' && github.repository_owner == 'silverstripe') || (github.event_name != 'schedule')
+    uses: silverstripe/gha-ci/.github/workflows/ci.yml@v1

.github/workflows/keepalive.yml

@@ -0,0 +1,17 @@
+name: Keepalive
+
+on:
+  # The 4th of every month at 11:20am UTC
+  schedule:
+    - cron: '20 11 4 * *'
+  workflow_dispatch:
+
+jobs:
+  keepalive:
+    name: Keepalive
+    # Only run cron on the silverstripe account
+    if: (github.event_name == 'schedule' && github.repository_owner == 'silverstripe') || (github.event_name != 'schedule')
+    runs-on: ubuntu-latest
+    steps:
+      - name: Keepalive
+        uses: silverstripe/gha-keepalive@v1

README.md

@@ -1,6 +1,6 @@
 # Introduction
 
-[![Build Status](https://travis-ci.com/silverstripe/api.silverstripe.org.svg?branch=master)](https://travis-ci.com/silverstripe/api.silverstripe.org)
+[![CI](https://github.com/silverstripe/api.silverstripe.org/actions/workflows/ci.yml/badge.svg)](https://github.com/silverstripe/api.silverstripe.org/actions/workflows/ci.yml)
 
 SilverStripe API docs for the core system in different versions,
 generated through [Doctum](https://github.com/code-lts/doctum#readme).