x/build/cmd/gopherbot: should not parse comments inside most markdown

[bradfitz]

In #36508 (comment) @ianlancetaylor told somebody how to remove a label later and put the instructions in backticks but gopherbot still parsed it.

It should try a bit to avoid finding directives in formatted text.

/cc @andybons @dmitshur @toothrot

[bradfitz]

And here's the opposite, also a parsing bug:

#36626 (comment)

... @ianlancetaylor tried to work around the parsing by adding lots of backticks to confuse gopherbot, but it confused it instead into parsing the gibberish as a request to add a label.

[dmitshur]

This also happened in #35482 (comment). /cc @toothrot

I agree gopherbot can be improved so it's easier to insert instructions for how to use it without unintentionally triggering said command. It's helpful to include data in this thread, so that any potential fix is easier to evaluate.

To share a workaround I tend to use, I rely on inserting zero-width space (https://en.wikipedia.org/wiki/Zero-width_space) inside the keywords when I want to explicitly prevent gopherbot from taking some action. For example:

@​gopher​bot ple​ase add label Waiting​ForInfo