[gnome-photos] flatpak: Change branch of libgdata to main

[Sam Thursfield <sthursfield src gnome org>]

commit 5baab17e11c66d9fa31388d5a788628a433e9a1e
Author: Manuel Wassermann <manuel wassermann97 gmail com>
Date:   Sun Jul 25 23:15:06 2021 +0200

    flatpak: Change branch of libgdata to main
    
    Fixes: #182

 flatpak/org.gnome.Photos.json | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/flatpak/org.gnome.Photos.json b/flatpak/org.gnome.Photos.json
index 443fb61e..39bdc617 100644
--- a/flatpak/org.gnome.Photos.json
+++ b/flatpak/org.gnome.Photos.json
@@ -137,6 +137,7 @@
             "sources": [
                 {
                     "type": "git",
+                    "branch": "main",
                     "url": "https://gitlab.gnome.org/GNOME/libgdata.git";
                 }
             ]