👌 IMPROVE: Allow Graph to be used by any backend

[chrisjsewell]

This is a follow-up to #5186,
to ensure Graph always uses the initialised Backend.

[chrisjsewell]

With this change, the Graph works correctly in #5145, for the archive backend, when no profile is loaded

[codecov]

Codecov Report

Merging #5200 (c225599) into develop (ea3ab28) will decrease coverage by 0.01%.
The diff coverage is 60.00%.

@@             Coverage Diff             @@
##           develop    #5200      +/-   ##
===========================================
- Coverage    81.00%   80.99%   -0.00%     
===========================================
  Files          535      535              
  Lines        37402    37404       +2     
===========================================
+ Hits         30292    30293       +1     
- Misses        7110     7111       +1     

Flag	Coverage Δ
django	75.82% <60.00%> (-<0.01%)	⬇️
sqlalchemy	74.92% <60.00%> (-<0.01%)	⬇️

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

Impacted Files	Coverage Δ
aiida/tools/visualization/graph.py	82.48% <60.00%> (-0.22%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ea3ab28...c225599. Read the comment docs.