FormPush: populate available remotes on changes

[DmitryZhelnin]

Fixes #4853

Proposed changes

• Populate remotes combobox in Push dialog after user modified available remotes

Test methodology

Manual testing

Test environment(s)

• Git Extensions 3.01.00.0
• Build 4695d0e (Dirty)
• Git 2.20.0.windows.1
• Microsoft Windows NT 6.1.7601 Service Pack 1
• .NET Framework 4.7.3221.0
• DPI 120dpi (125% scaling)

[RussKie]

👍

[codecov]

Codecov Report

Merging #6130 into master will decrease coverage by 0.52%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #6130      +/-   ##
==========================================
- Coverage   44.61%   44.09%   -0.53%     
==========================================
  Files         648      648              
  Lines       49232    49228       -4     
  Branches     6567     6567              
==========================================
- Hits        21965    21707     -258     
- Misses      26022    26332     +310     
+ Partials     1245     1189      -56

[RussKie]

Thank you