Fix provider fallback list

[ml-evs]

Closes #829

[codecov]

Codecov Report

Merging #830 (04a3850) into master (2e9507e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #830   +/-   ##
=======================================
  Coverage   92.68%   92.68%           
=======================================
  Files          68       68           
  Lines        3759     3759           
=======================================
  Hits         3484     3484           
  Misses        275      275           

Flag	Coverage Δ
project	92.68% <ø> (ø)
validator	92.68% <ø> (ø)

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Impacted Files	Coverage Δ
optimade/server/routers/utils.py	98.51% <ø> (ø)

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[ml-evs]

I am going to take executive action and merge this one myself...