GDBus: Note distros whose GDBusServers require an initial response

Ideally, we would eventually move to always using the
cross-namespace-friendly authentication handshake and never sending an
initial response with the Unix uid or Windows SID, but that's blocked
on waiting for various LTS OS distributions to become unsupported or
otherwise irrelevant. Make a note of some major LTS distributions that
still have an old version that is missing glib!2826.

In the RHEL/CentOS family, CentOS Stream 10 has a fixed version, so
presumably RHEL 10 will have a fixed version when it is released.

In the Debian family, Debian 12 and Ubuntu 24.04 are stable releases
that contain a fixed version.

In the SUSE family, openSUSE 15.6 contains a fixed version, so
presumably so does SLES 15.6.

Faster-moving distributions like Fedora are not a concern here and
can be ignored: it's always the slow-moving and/or LTS distributions
that are going to be holding back interoperability breaks.

Signed-off-by: Simon McVittie <smcv@collabora.com>

gio/gdbusauthmechanismexternal.c

@@ -387,8 +387,8 @@ mechanism_client_initiate (GDBusAuthMechanism   *mechanism,
   else
     {
       /* Send the Unix uid or Windows SID as an initial response.
-       * This is the only thing that is interoperable with GDBus 2.73.3
-       * servers. */
+       * This is the only thing that is interoperable with GDBus < 2.73.3
+       * servers (RHEL ≤ 9, Debian ≤ 11, Ubuntu ≤ 22.04, SUSE ≤ 15.5). */
 #if defined(G_OS_UNIX)
       GCredentials *credentials;