[misc] fix ci -- pin fake-gcs to a compatible version

services/docstore/docker-compose.ci.yml

@@ -56,7 +56,7 @@ services:
       interval: 1s
       retries: 20
   gcs:
-    image: fsouza/fake-gcs-server
+    image: fsouza/fake-gcs-server:v1.21.2
     command: ["--port=9090", "--scheme=http"]
     healthcheck:
       test: wget --quiet --output-document=/dev/null http://localhost:9090/storage/v1/b

services/docstore/docker-compose.yml

@@ -55,7 +55,7 @@ services:
       retries: 20
 
   gcs:
-    image: fsouza/fake-gcs-server
+    image: fsouza/fake-gcs-server:v1.21.2
     command: ["--port=9090", "--scheme=http"]
     healthcheck:
       test: wget --quiet --output-document=/dev/null http://localhost:9090/storage/v1/b