Fix incomplete logged sentence in SocketModeReciever

[khrj]

Summary

-this.logger.error(`Tried to reach ${req.url} which isn't a`);	
+this.logger.error(`Tried to reach ${req.url} which isn't a valid route.`);

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

Merging #807 (d3b610c) into main (ea5adc9) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##             main     #807   +/-   ##
=======================================
  Coverage   65.47%   65.47%           
=======================================
  Files          11       11           
  Lines        1089     1089           
  Branches      323      323           
=======================================
  Hits          713      713           
  Misses        317      317           
  Partials       59       59           

Impacted Files	Coverage Δ
src/receivers/SocketModeReceiver.ts	9.80% <0.00%> (ø)

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[seratch]

Thanks, the change looks good to me. Other maintainers will check this early next week.