Migrate staging job to GitHub Actions; remove CircleCI

We are officially at the end of the road for the CircleCI to GitHub
Actions migration! This migrates the final job over and removes the
manifest entirely.

The staging credentials have already been configured by infra, all that
was needed was adjusting some of the `$CIRCLE_` environment variables. I
added a bit of output to aid future debugging.

Fixes #6886.

.github/workflows/staging.yml

@@ -0,0 +1,23 @@
+name: Staging
+on:
+  push:
+    branches:
+      - 'stg-*'
+      - 'release/*'
+  schedule:
+    - cron: '0 3 * * *'
+
+jobs:
+  staging:
+    runs-on: ubuntu-latest
+    env:
+      GOOGLE_CREDENTIALS: ${{ secrets.GOOGLE_CREDENTIALS }}
+    steps:
+      - uses: actions/checkout@v4
+      - name: Run staging tests on GCE
+        run: |
+          make ci-go
+      - name: Teardown (if needed)
+        if: always()
+        run: |
+          make ci-teardown || true

devops/gce-nested/ci-env.sh

@@ -4,16 +4,16 @@
 
 # If these scripts are run on developer workstations, the CI env
 # vars populated by CircleCI won't be present; make a sane default.
-if [ -z "${CIRCLE_BUILD_NUM:-}" ]; then
-    export CIRCLE_BUILD_NUM="${USER}"
+if [ -z "${GITHUB_RUN_ID:-}" ]; then
+    export GITHUB_RUN_ID="${USER}"
 fi
 
 # Set common vars we'll need throughout the CI scripts.
 TOPLEVEL="$(git rev-parse --show-toplevel)"
 export TOPLEVEL
 GCE_CREDS_FILE="${TOPLEVEL}/.gce.creds"
 export GCE_CREDS_FILE
-export BUILD_NUM="${CIRCLE_BUILD_NUM}"
+export BUILD_NUM="${GITHUB_RUN_ID}-${GITHUB_RUN_ATTEMPT}"
 export PROJECT_ID="securedrop-ci"
 export JOB_NAME="sd-ci-nested"
 export GCLOUD_MACHINE_TYPE="c2-standard-8"

devops/gce-nested/gce-start.sh

@@ -46,6 +46,7 @@ function create_sd_ci_gce_instance() {
           --metadata "ssh-keys=${SSH_USER_NAME}:$(cat $SSH_PUBKEY)"
 
       # Give box a few more seconds for SSH to become available
+      echo "Sleeping for 20s to wait for SSH to become available"
       sleep 20
   fi
 }

devops/gce-nested/gce-stop.sh

@@ -11,4 +11,4 @@ TOPLEVEL="$(git rev-parse --show-toplevel)"
 . "${TOPLEVEL}/devops/gce-nested/ci-env.sh"
 
 # Destroy remote instance
-gcloud_call --quiet compute instances delete "${JOB_NAME}-${BUILD_NUM}"
+gcloud_call compute instances delete "${JOB_NAME}-${BUILD_NUM}"