fix: Update getting value usage.

[VVildVVolf]

Description

Update getting value of select2 according to their recomendation: https://github.com/select2/select2/blob/4de1d236e602149a5c78d35899b49b3989b94107/src/js/select2/core.js#L536

ADDITIONAL INFORMATION

• Has associated issue:
• Is CRUD MVC related.
• Is Auth, RBAC security related.
• Changes the security db schema.
• Introduces new feature
• Removes existing feature

[codecov]

Codecov Report

Merging #2039 (95d0aeb) into master (0e08270) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2039      +/-   ##
==========================================
+ Coverage   78.46%   78.52%   +0.05%     
==========================================
  Files          72       72              
  Lines        8685     8698      +13     
==========================================
+ Hits         6815     6830      +15     
+ Misses       1870     1868       -2     

Flag	Coverage Δ
python	78.52% <100.00%> (+0.05%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flask_appbuilder/models/sqla/interface.py	81.92% <ø> (ø)
flask_appbuilder/views.py	66.11% <ø> (ø)
flask_appbuilder/cli.py	61.18% <100.00%> (+2.25%)	⬆️

... and 1 file with indirect coverage changes

[dpgaspar]

Nice, thanks