BasisLieHighestWeight: Rename some variables in doctests

[lgoettgens]

As per request of @gfourier.

The previous code raised the following error when copy-pasted in a session after using Oscar:

ERROR: cannot assign a value to imported variable Oscar.bases from module Main
Stacktrace:
 [1] top-level scope
   @ REPL[13]:1

Renaming the local variable gets rid of this issue and makes it easier for people to play around with the code

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.41%. Comparing base (7219bae) to head (5b85f83).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4461   +/-   ##
=======================================
  Coverage   84.41%   84.41%           
=======================================
  Files         668      668           
  Lines       88441    88441           
=======================================
  Hits        74656    74656           
  Misses      13785    13785           

Files with missing lines	Coverage Δ
...imental/BasisLieHighestWeight/src/UserFunctions.jl	92.30% <ø> (ø)