Run Rust CI only if rust directory is modified

[cijothomas]

Avoid running CI checks unnecessarily. Need to validate if this causes any issue with "required check". Hopefully not, as this is a pattern used in other OTel repos too.

Later to be expanded to Go also.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.48%. Comparing base (dfca971) to head (a3ac447).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1529      +/-   ##
==========================================
- Coverage   83.50%   83.48%   -0.02%     
==========================================
  Files         428      428              
  Lines      119410   119410              
==========================================
- Hits        99713    99691      -22     
- Misses      19163    19185      +22     
  Partials      534      534              

Components	Coverage Δ
otap-dataflow	84.67% <ø> (-0.04%)	⬇️
query_abstraction	80.61% <ø> (ø)
query_engine	90.26% <ø> (ø)
syslog_cef_receivers	∅ <ø> (∅)
otel-arrow-go	53.50% <ø> (ø)

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[drewrelmas]

Unfortunately, my intuition is that this will break due to required checks. Do you have an example from other opentelemetry repos showing that is not the case?

[cijothomas]

Unfortunately, my intuition is that this will break due to required checks. Do you have an example from other opentelemetry repos showing that is not the case?

It should not break. open-telemetry/opentelemetry-dotnet#5023 is when we tried this in .NET by @CodeBlanch !

[jmacd]

(We'll see if it breaks!)