ci: use github actions for ci

.github/workflows/ci.yml

@@ -0,0 +1,20 @@
+name: CI
+on: push
+jobs:
+  CI:
+    name: Continuous Integration
+    runs-on: ubuntu-latest
+    permissions:
+      # required by guardian/actions-assume-aws-role
+      id-token: write
+      contents: read
+    steps:
+      - uses: actions/checkout@v2
+      - uses: guardian/actions-assume-aws-role@v1.0.0
+        with:
+          awsRoleToAssume: ${{ secrets.GU_RIFF_RAFF_ROLE_ARN }}
+      - uses: actions/setup-node@v2
+        with:
+          node-version-file: '.nvmrc'
+          cache: 'yarn'
+      - run: ./ci.sh

ci.sh

@@ -2,7 +2,19 @@
 
 set -ae
 
+# This block can be removed once everyone has rebase their branches to main
+if [[ ! -z "${TEAMCITY_VERSION}" ]]; then
+  echo "Running in TeamCity. Nope!"
+  exit 0
+fi
+
+# Don't remove this line as it's used to number the build based on the
+# last build number in teamcity
+LAST_TEAMCITY_BUILD=5000
+export GITHUB_RUN_NUMBER=$(( $GITHUB_RUN_NUMBER + $LAST_TEAMCITY_BUILD ))
+
 yarn install --frozen-lockfile
 yarn lint
 yarn test
 yarn build
+yarn riffraff