Update to 2.70.3

• Several important fixes to FD handling in gspawn (#2503, #2506, #2580)
• Several important fixes to GDBus message and GVariant parsing of invalid data (#2557, #2572)
• Fix potential data loss due to missing fsync when saving files on btrfs (!2437)

Bugs fixed:

• 2503 gspawn.c may clobber target fds
• 2506 gspawn.c fails to close child_err_report_fd if it is duped to avoid conflation with one of the target_fds
• 2557 Arrays of zero-element tuples with non-zero length lead to infinite loops in g_dbus_message_new_from_blob
• 2572 Check for GVariant recursion depth before recursing
• 2580 gspawn doesn't set CLOEXEC if close_range fails unexpectedly
• !2394 Backport !1968 “gspawn: Fix file descriptor conflation issues” to glib-2-70
• !2415 Backport !2412 “paramspec: fix unref annotation” to glib-2-70
• !2437 Backport !2425 “gfileutils: Remove outdated BTRFS fsync optimization from set_contents” to glib-2-70
• !2444 Backport !2435 “gspawn: Report errors with closing file descriptors between fork/exec” to glib-2-70
• !2455 Backport !2454 gdbusmessage and gvariant fixes to glib-2-70