package/webkitgtk: security bump to version 2.38.5

Bugfix release, with many security fixes, including (but not limited to)
a patch for CVE-2023-23529.

Release notes:

  https://webkitgtk.org/2023/02/15/webkitgtk2.38.5-released.html

Accompanying security advisory:

  https://webkitgtk.org/security/WSA-2023-0002.html

Also raise the minimal GCC version to 8.3, which was already required since webkitgtk-2.36.4.
Similar to commit ec1ff802,
we do check on >= GCC 8, because we can't check on >= GCC 8.3.

  https://github.com/WebKit/WebKit/commit/f812c5db1ff22bcbe1070ca4ed613085cd36499b



Signed-off-by: Thomas Devoogdt <thomas.devoogdt@gmail.com>
Acked-by: Adrian Perez de Castro <aperez@igalia.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>