regression: Department's unit field becomes disabled after selecting a unit

[aleksandernsilva]

Proposed changes (including videos or screenshots)

This PR fixes a bug where the unit field in the EditDepartment page becomes disabled immediately after selecting a unit. The field should only become disabled after a unit has been set and saved.

Now, the field remains editable until the department is saved, ensuring users can freely change the business unit while creating a department.

Issue(s)

CTZ-22

Steps to test or reproduce

• Access Enterprise workspace
• Go Omnichannel > Department
• New department
• Field "Unit" should be visible
• Select a unit
• Field should remain enabled
• Save and edit
• Unit field should be disabled

Further comments

Introduced here: #35370

[dionisio-bot]

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[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.72%. Comparing base (cc4111c) to head (9ce23a8).
Report is 1 commits behind head on release-7.5.0.

Additional details and impacted files

@@              Coverage Diff               @@
##           release-7.5.0   #35581   +/-   ##
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  Coverage          59.72%   59.72%           
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  Files               2832     2832           
  Lines              68886    68886           
  Branches           15280    15280           
==============================================
  Hits               41144    41144           
  Misses             25066    25066           
  Partials            2676     2676           

Flag	Coverage Δ
unit	75.92% <ø> (ø)

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