Use a fixed git abbrev parameter when we fetch a git revision

changelogs/unreleased/10735-geo-gitlab-revision-can-return-not-consistent-results.yml

+---
+title: Use a fixed git abbrev parameter when we fetch a git revision
+merge_request: 26707
+author:
+type: fixed

lib/gitlab.rb

@@ -24,7 +24,7 @@ module Gitlab
       if File.exist?(root.join("REVISION"))
         File.read(root.join("REVISION")).strip.freeze
       else
-        result = Gitlab::Popen.popen_with_detail(%W[#{config.git.bin_path} log --pretty=format:%h -n 1])
+        result = Gitlab::Popen.popen_with_detail(%W[#{config.git.bin_path} log --pretty=format:%h --abbrev=11 -n 1])
 
         if result.status.success?
           result.stdout.chomp.freeze

spec/lib/gitlab_spec.rb

@@ -10,7 +10,7 @@ describe Gitlab do
   end
 
   describe '.revision' do
-    let(:cmd) { %W[#{described_class.config.git.bin_path} log --pretty=format:%h -n 1] }
+    let(:cmd) { %W[#{described_class.config.git.bin_path} log --pretty=format:%h --abbrev=11 -n 1] }
 
     around do |example|
       described_class.instance_variable_set(:@_revision, nil)