fix: runtimeConfigModule config validation

[arcanis]

It seems like the validation got stricter, and runtimeConfigModule alternative syntax (#895) wasn't covered.

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[codecov]

Codecov Report

Merging #972 (f072b9c) into main (b9683cc) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #972   +/-   ##
=======================================
  Coverage   83.30%   83.30%           
=======================================
  Files          53       53           
  Lines        1605     1605           
  Branches      430      430           
=======================================
  Hits         1337     1337           
  Misses        156      156           
  Partials      112      112           

Impacted Files	Coverage Δ
packages/conf/src/index.ts	80.51% <ø> (ø)

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[semoal]

Thanks you so much Maël! Much appreciated