chore: fix git_sha in instance health (#8893)

- Fix git-hash in super admin instance health page for Heroku installations
- Fix git boundary not set error for docker/heroku deployments which remove .git directory

app/controllers/super_admin/instance_statuses_controller.rb

@@ -28,8 +28,7 @@ class SuperAdmin::InstanceStatusesController < SuperAdmin::ApplicationController
   end
 
   def sha
-    sha = `git rev-parse HEAD`
-    @metrics['Git SHA'] = sha.presence || 'n/a'
+    @metrics['Git SHA'] = GIT_HASH
   end
 
   def postgres_status