pkg/opensuse: switch to SHA1 fork

src.opensuse.org switched to SHA256, which means it can no longer be
used as a submodule in a SHA1 repository. Switch to a fork on Pagure
that gets synced across and is still SHA1:

https://code.opensuse.org/package/systemd.git

.gitmodules

@@ -4,8 +4,8 @@
 	branch = rawhide
 [submodule "pkg/opensuse"]
 	path = pkg/opensuse
-	url = https://src.opensuse.org/rpm/systemd.git
-	branch = factory
+	url = https://code.opensuse.org/package/systemd.git
+	branch = master
 [submodule "pkg/debian"]
 	path = pkg/debian
 	url = https://salsa.debian.org/systemd-team/systemd.git