FI-2664: Prevent validator sessions from being created in test environment

[Jammjammjamm]

This prevents validator sessions from being created in the test environment. The validator is not expected to be running during unit tests, so it will not be reachable. By default, the validator is going to be using a docker hostname, which causes a DNS error when trying to create a session, preventing unit tests from running in test kits which use the new validator. This happens when Inferno boots (i.e. prior to unit test execution), so this can't be handled by stubbing the requests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.74%. Comparing base (3047f95) to head (47cfeef).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #477      +/-   ##
==========================================
- Coverage   77.77%   77.74%   -0.04%     
==========================================
  Files         234      234              
  Lines       11622    11623       +1     
  Branches     1095     1096       +1     
==========================================
- Hits         9039     9036       -3     
- Misses       1963     1967       +4     
  Partials      620      620              

Flag	Coverage Δ
backend	93.96% <100.00%> (-0.12%)	⬇️
frontend	70.77% <ø> (ø)

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