BlueBrainNexusStore: fix updating schemas

[MFSY]

• BlueBrainNexusStore: updating schemas required a specific schema URI to be present in the request URL or '_' in case of UNCONSTRAINED resources

[codecov-commenter]

Codecov Report

Merging #331 (dcf3555) into master (876c3f8) will increase coverage by 0.05%. The diff coverage is 81.81%.

@@            Coverage Diff             @@
##           master     #331      +/-   ##
==========================================
+ Coverage   72.81%   72.87%   +0.05%     
==========================================
  Files          90       90              
  Lines        5794     5802       +8     
==========================================
+ Hits         4219     4228       +9     
+ Misses       1575     1574       -1     

Flag	Coverage Δ
unittests	72.87% <81.81%> (+0.05%)	:arrow_up:

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

Files Changed	Coverage Δ
kgforge/specializations/stores/bluebrain_nexus.py	27.94% <0.00%> (+0.05%)	:arrow_up:
kgforge/specializations/stores/nexus/service.py	55.51% <81.81%> (+0.75%)	:arrow_up:
...sts/specializations/stores/test_bluebrain_nexus.py	93.86% <100.00%> (+0.15%)	:arrow_up: