* fix(xml): no-op when predicated xpath finds no match instead of creating nodes
When using xpath like element[text()='old'] with value=new, a no-match due
to the predicate not being satisfied incorrectly triggered node creation,
corrupting the XML. Now treats predicate misses as a no-op.
Fixes#8730
* changelog(xml): add fragment for PR #12031
* fix(xml): remove spurious test-unset-element-value include from main.yml
That file belongs to a different branch and was accidentally dragged in
during a stash conflict resolution.
* feat(xml): add create_if_missing option to control node creation on value no-match
Instead of implicitly creating nodes when value is set and xpath finds no match,
expose create_if_missing (default true, preserving old behavior) so callers
can opt into a silent no-op with create_if_missing=false.
Fixes#8730
