fix comment regarding invalid annotation handling

[kzc]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

#4068

Description

Fix comment in #4068 and add an example of an invalid annotation.
No code changes.

[github-actions]

Thank you for your contribution! ❤️

You can try out this pull request locally by installing Rollup via

npm install kzc/rollup#fix-comment-for-invalid-annotation

or load it into the REPL:
https://rollupjs.org/repl/?pr=4081

[codecov]

Codecov Report

Merging #4081 (e575d47) into master (2bee261) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4081   +/-   ##
=======================================
  Coverage   97.49%   97.49%           
=======================================
  Files         193      193           
  Lines        6818     6824    +6     
  Branches     2002     2005    +3     
=======================================
+ Hits         6647     6653    +6     
  Misses         84       84           
  Partials       87       87           

Impacted Files	Coverage Δ
src/Graph.ts	100.00% <100.00%> (ø)
src/utils/pureComments.ts	100.00% <100.00%> (ø)

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