Fix some typos in graph.h doc strings

[zdavkeos]

[github-actions[bot]]

Marking this PR as stale. It will not be automatically closed.

Even though the maintainers of Graaf may not always have time to take a look in a timely fashion, your contributions are much appreciated. Please allow some time for @bobluppes to take a closer look.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.57%. Comparing base (d1a7873) to head (ebeb2cb).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #209   +/-   ##
=======================================
  Coverage   99.57%   99.57%           
=======================================
  Files          56       56           
  Lines        2586     2586           
  Branches      135      135           
=======================================
  Hits         2575     2575           
  Misses         11       11           

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.