Fix small typo in goto-harness documentation

[hannes-steffenhagen-diffblue]

• Each commit message has a non-empty body, explaining why the change was made.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[chrisr-diffblue]

Nice catch :-)

[codecov-io]

Codecov Report

Merging #5243 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #5243   +/-   ##
========================================
  Coverage    67.43%   67.43%           
========================================
  Files         1162     1162           
  Lines        95620    95620           
========================================
  Hits         64477    64477           
  Misses       31143    31143

Flag	Coverage Δ
#cproversmt2	42.59% <ø> (ø)	⬆️
#regression	63.96% <ø> (ø)	⬆️
#unit	31.89% <ø> (ø)	⬆️

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