spec: Add missing GLib dependency when building without DNF

GLib is required to build rhsmcertd(8).  When building with DNF support,
glib2-devel is pulled in by libdnf-devel.  However, turning off DNF
support doesn't disable building rhsmcertd(8).  Therefore, the depedency
needs to be listed explicitly.

subscription-manager.spec

@@ -186,6 +186,7 @@ BuildRequires: openssl-devel
 BuildRequires: gcc
 BuildRequires: %{py_package_prefix}-setuptools
 BuildRequires: gettext
+BuildRequires: glib2-devel
 
 %if 0%{?suse_version}
 BuildRequires: distribution-release