Fix : tree rank picklist validation after async data loads

[Gitesh307]

Fixes #7511

This PR restores the tree level picklist to its pre-regression behavior so editing existing tree nodes no longer triggers the browser’s “Please select an item in the list” error.

Checklist

• Self-review the PR after opening it to make sure the changes look good and
  self-explanatory (or properly documented)
• Add relevant issue to release milestone

Testing instructions

• open an existing non-root tree node, and confirm the Level field stays valid and Save button is not red anymore, other buttons stays enabled without re-selecting the rank.
• verify that non-typeable behavior for tree level rank picklist is working.

[Iwantexpresso]

• open an existing non-root tree node, and confirm the Level field stays valid and Save button is not red anymore, other buttons stays enabled without re-selecting the rank.

• just tested it and it looks good!

[emenslin]

• open an existing non-root tree node, and confirm the Level field stays valid and Save button is not red anymore, other buttons stays enabled without re-selecting the rank.

Looks good, buttons are no longer red!

[CarolineDenis]

@Gitesh307, do you know when this code was changed and why?

[Gitesh307]

@Gitesh307, do you know when this code was changed and why?

The change was introduced when I added the fix to disable manual typing in tree-level rank picklists issue #4985. That fix unintentionally treated _treeLevelComboBox like the others, which moved it to a simple dropdown and broke validation that depends on async data loading. So the condition was updated to exclude _treeLevelComboBox, letting it keep AutoComplete behavior and resolving the validation issue in #7524 .

[Gitesh307]

The PR now initializes as valid and Save is enabled without allowing manual typing. Both validation and non-typeable behavior for tree level rank picklist (issue-4985) are intact.