[gnome-shell] git: Use relative URL for external submodule

[Marge Bot <marge-bot src gnome org>]

commit c865d1b414e3df41a3d708aeb33b6aed3960abca
Author: Florian Müllner <fmuellner gnome org>
Date:   Sun Jul 10 22:12:37 2022 +0200

    git: Use relative URL for external submodule
    
    Gitlab recommends using relative URLs for submodules on the same
    server[0], so do that.
    
    [0] https://docs.gitlab.com/ee/ci/git_submodules.html
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2371>

 .gitmodules | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitmodules b/.gitmodules
index 5ab4a386da..aa33bbb911 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,3 @@
 [submodule "subprojects/gvc"]
        path = subprojects/gvc
-       url = https://gitlab.gnome.org/GNOME/libgnome-volume-control.git
+       url = ../libgnome-volume-control.git