expat: upgrade to 2.7.2

expat: upgrade to 2.7.2

Primarily to fix CVE-2025-59375 (Disallow use of disproportional amounts
of dynamic memory from within an Expat parser) but the full list of
changes are available:

https://github.com/libexpat/libexpat/blob/R_2_7_2/expat/Changes

(From OE-Core rev: fbe5f76ba6af0983cd90a05d4077e453e2ebb475)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Yogita Urade <yogita.urade@windriver.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>