Ignore check_stack_overrun function in optimization test in rpminspect
check.
This function is purposely not being optimized, to preserve a
stack variable creation.
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Resolves: #2012938
Reason is, that the bug is already reported on upstream:
https://jira.mariadb.org/browse/MDEV-26905.
Also we currently do not know how to fix it. If we eventually figure out
how to fix this bug, then the patch would be submitted directly to the
upstream, rather than to downstream, to avoid unintentionally breaking
some code that relied on the malformed XML.