Fix Mix warning about missing :opentelemetry app when MIX_TARGET != application

[alco]

The problem got introduced in 03c10a2#diff-e39d5a2dccf3960074b1107d725583e91ddc8599a7643f63144df19981bc3c6e.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.21%. Comparing base (03c10a2) to head (dc440d4).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3557      +/-   ##
==========================================
- Coverage   75.36%   75.21%   -0.15%     
==========================================
  Files          51       51              
  Lines        2744     2744              
  Branches      404      405       +1     
==========================================
- Hits         2068     2064       -4     
- Misses        674      678       +4     
  Partials        2        2              

Flag	Coverage Δ
electric-telemetry	22.71% <ø> (ø)
elixir	57.38% <ø> (-0.36%)	⬇️
elixir-client	73.94% <ø> (-0.53%)	⬇️
packages/experimental	87.73% <ø> (ø)
packages/react-hooks	86.48% <ø> (ø)
packages/typescript-client	93.08% <ø> (ø)
packages/y-electric	55.12% <ø> (ø)
typescript	87.46% <ø> (ø)
unit-tests	75.21% <ø> (-0.15%)	⬇️

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