libxml2: Upgrade 2.12.6 -> 2.12.8

CVE's Fixed by upgrade:
CVE-2024-34459 libxml2: buffer over-read in xmlHTMLPrintFileContext in xmllint.c

Other Changes between 2.12.6 -> 2.12.8
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https://gitlab.gnome.org/GNOME/libxml2/-/blob/2.12/NEWS?ref_type=heads



Signed-off-by: Siddharth Doshi <sdoshi@mvista.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>