coin: use internal mirror of git-repo

Cloning from github have been failing recently, use internal
mirror of google's git-repo instead.

Change-Id: I3983812c59be601632c3e27b6aab00c0e09ce037
Reviewed-by: Mikko Gronoff <mikko.gronoff@qt.io>
(cherry picked from commit 76cbb93c22)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 4801c53e39)
(cherry picked from commit b5c2cfa8d5)

coin/module_config.yaml

@@ -137,7 +137,7 @@ instructions:
       chmod +x repo
 
       ./repo init \
-          --repo-url https://github.com/theqtcompany/git-repo \
+          --repo-url git@git.qt.io:boot2qt/git-repo.git \
           -u git://code.qt.io/yocto/boot2qt-manifest \
           -b ci \
           -m ${MANIFEST} \