gitlab: use git version 2.10.2

An issue on Gitlab SR when pushing on protected branches occurs with git 2.11.
Gitlab issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/25601

software/gitlab/software.cfg

@@ -62,6 +62,10 @@ parts =
 [slapos.cookbook-repository]
 revision = 571d6514f7290e8faa9439c4b86aa2f6c87df261
 
+[git]
+# TODO stop using custom git revision once git 2.11 is supported by Gitlab
+url = https://www.kernel.org/pub/software/scm/git/git-2.10.2.tar.xz
+md5sum = 3cd1dca37be60668f482545716923b72
 
 ############################
 #   Software compilation   #