add GetJuliaScratchspace to JuliaInterface

[ThomasBreuer]

This is the non-controversial part of #1026.

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 76.75%. Comparing base (a8674da) to head (8d8c8cb).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/utils.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1030      +/-   ##
==========================================
+ Coverage   76.73%   76.75%   +0.02%     
==========================================
  Files          51       51              
  Lines        4182     4191       +9     
==========================================
+ Hits         3209     3217       +8     
- Misses        973      974       +1     

Files with missing lines	Coverage Δ
pkg/JuliaInterface/gap/JuliaInterface.gd	100.00% <100.00%> (ø)
pkg/JuliaInterface/gap/JuliaInterface.gi	94.39% <100.00%> (+0.39%)	⬆️
src/utils.jl	48.48% <0.00%> (-1.52%)	⬇️