Fix: Do not set the transaction to scope if no op

[marandaneto]

📜 Description

Fix: Do not set the transaction to scope if no op

💡 Motivation and Context

Closes #826

💚 How did you test it?

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• I updated the docs if needed
• All tests passing
• No breaking changes

🔮 Next steps

[codecov-commenter]

Codecov Report

Merging #828 (95ae670) into main (9cd2c20) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #828   +/-   ##
=======================================
  Coverage   89.83%   89.84%           
=======================================
  Files         114      114           
  Lines        3670     3672    +2     
=======================================
+ Hits         3297     3299    +2     
  Misses        373      373           

Impacted Files	Coverage Δ
.../lib/src/navigation/sentry_navigator_observer.dart	98.75% <100.00%> (+0.03%)	⬆️

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[denrase]

LGTM