Fix a bug in docker_push.sh, and indent in .cirrus.yml (#20308)

diff --git a/.cirrus.yml b/.cirrus.yml
index ea9b7e4..a8f6c06 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -121,8 +121,8 @@
   osx_instance:
     image: high-sierra-xcode-9.4.1
   git_fetch_script:
-  - git fetch origin
-  - git fetch origin master # To set FETCH_HEAD
+    - git fetch origin
+    - git fetch origin master # To set FETCH_HEAD
   setup_script:
     - bin/flutter config --no-analytics
     - bin/flutter update-packages