gitlab-ci: check-dco.py: switch from master to stable-7.2 branch

There's one commit, tagged v7.2.2, without Signed-off-by line.
Due to this, check-dco test always fail on 7.2.  Since this is
a stable branch with almost all commits coming from master
already with S-o-b (except of the version bumps and very rare
stable-specific commits), and v7.2.2 is already cast in stone,
let's base the check on stable-7.2 branch (with its last version)
instead of master branch.  This way, staging-7.2 will be checked
against stable-7.2, but stable-7.2 itself will not be checked
anymore, - so we can catch errors during stable preparations.

Note: this is a change specific to stable-7.2 branch/series, it
is not supposed to be in master.

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

.gitlab-ci.d/check-dco.py

@@ -20,12 +20,12 @@
 repourl = "https://gitlab.com/%s/%s.git" % (namespace, reponame)
 
 subprocess.check_call(["git", "remote", "add", "check-dco", repourl])
-subprocess.check_call(["git", "fetch", "check-dco", "master"],
+subprocess.check_call(["git", "fetch", "check-dco", "stable-7.2"],
                       stdout=subprocess.DEVNULL,
                       stderr=subprocess.DEVNULL)
 
 ancestor = subprocess.check_output(["git", "merge-base",
-                                    "check-dco/master", "HEAD"],
+                                    "check-dco/stable-7.2", "HEAD"],
                                    universal_newlines=True)
 
 ancestor = ancestor.strip()
@@ -85,7 +85,7 @@
 
 To bulk update all commits on current branch "git rebase" can be used:
 
-  git rebase -i master -x 'git commit --amend --no-edit -s'
+  git rebase -i stable-7.2 -x 'git commit --amend --no-edit -s'
 
 """)