fix(alerting): correct success threshold for telegram

[plantatorbob]

Summary

There is a typo in Telegram alerting provider implementation: for resolved alerts, instead of success count, failure count is printed instead.

This PR fixes the typo and adjusts relevant test cases.

Checklist

• Tested and/or added tests to validate that the changes work as intended, if applicable.
• Updated documentation in README.md, if applicable.

[TwiN]

Good catch!

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (5c5a954) 81.02% compared to head (50fa3a7) 81.02%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #551   +/-   ##
=======================================
  Coverage   81.02%   81.02%           
=======================================
  Files          56       56           
  Lines        4391     4391           
=======================================
  Hits         3558     3558           
- Misses        650      651    +1     
+ Partials      183      182    -1     

Files Changed	Coverage Δ
alerting/provider/telegram/telegram.go	83.63% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[TwiN]

Thank you for the contribution!