Fixed two linter errors for dynamical semigroups

[MatheMagicianPi]

Resolves two linter errors

1. Fixes type comparison by using isinstance()
2. Fixes doc string formatting error

Fixes two linter issues originating from #35988
This is part of issue #35954

📝 Checklist

• The title is concise, informative, and self-explanatory.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation accordingly.

⌛ Dependencies

• Implemented five new operations for dynamical semigroups #35988: origin of linter errors
• Initial implementation of dynamical semigroups #35947: dependency of Implemented five new operations for dynamical semigroups #35988

[EnderWannabe]

Looks like @fchapoton has authored a pull request to fix the all the current linter issues, so this pull request is not necessary. Thank you Frédéric!

[github-actions]

Documentation preview for this PR (built with commit f746342; changes) is ready! 🎉

[fchapoton]

please look at #36148 and confirm that my fix is ok for you

[mkoeppe]

Duplicate of #36148