ci: pull cloud-sdk emulator image from getsentry/image-mirror (#681)

`google/cloud-sdk` (implicit `latest`) →
`ghcr.io/getsentry/image-mirror-google-cloud-sdk:588.0.0`, which is what
`latest` resolves to today. Changed in the Bigtable emulator step in
`.github/workflows/ci.yml` and in `devservices/config.yml`.

**Why:** `Test (all features)` has been failing on anonymous Docker Hub
pulls (`auth.docker.io` timeouts and 429s) from GitHub-hosted runners.

**Depends on** getsentry/image-mirror#37 being merged and synced.
`588.0.0` is amd64-only upstream, same as before.

**Related:** the GCS emulator is built from
`getsentry/google-cloud-storage-testbench#main`, whose `FROM
python:3.12@sha256:…` is also on Docker Hub. There's a separate draft PR
in that repo.

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via @joshuarli.
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Co-authored-by: sentry-junior[bot] <264270552+sentry-junior[bot]@users.noreply.github.com>
Co-authored-by: Joshua Li <14209781+joshuarli@users.noreply.github.com>

Author: sentry-junior[bot]

.github/workflows/ci.yml

@@ -98,7 +98,7 @@ jobs:
             -p 8086:8086 \
             -e BIGTABLE_EMULATOR_HOST=localhost:8086 \
             -v $PWD/devservices/run-bigtable.sh:/run-bigtable.sh \
-            google/cloud-sdk \
+            ghcr.io/getsentry/image-mirror-google-cloud-sdk:588.0.0 \
             /run-bigtable.sh
 
       - name: Build GCS Emulator

devservices/config.yml

@@ -44,7 +44,7 @@ services:
       - orchestrator=devservices
     restart: unless-stopped
   bigtable:
-    image: google/cloud-sdk
+    image: ghcr.io/getsentry/image-mirror-google-cloud-sdk:588.0.0
     command: /run-bigtable.sh
     environment:
       BIGTABLE_EMULATOR_HOST: localhost:8086