Fix GHTeam#remove(GHUser) and add tests

[gsmet]

I included the original commit of #1437 with the original author (just reworded the commit message for more clarity).

My advice would be to release something right away as this could be considered as a security issue given we are not removing people from teams appropriately.

Note that it was broken anyway since GH retired the old Teams API.

[codecov]

Codecov Report

Merging #1438 (d870d21) into main (0365965) will increase coverage by 0.12%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main    #1438      +/-   ##
============================================
+ Coverage     78.65%   78.77%   +0.12%     
- Complexity     2097     2100       +3     
============================================
  Files           201      201              
  Lines          6389     6390       +1     
  Branches        359      359              
============================================
+ Hits           5025     5034       +9     
+ Misses         1157     1149       -8     
  Partials        207      207              

Impacted Files	Coverage Δ
src/main/java/org/kohsuke/github/GHTeam.java	83.52% <100.00%> (+9.71%)	⬆️

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[gsmet]

Thanks for the quick release @bitwiseman !