Simple fixes for checkdoc and byte compiler

[sje30]

Hi,
I've made a few docstring edits to pass checkdoc and also byte compiler warnings.

There are some remaining 'byte compiler' warnings, below. Would you be interested in a patch to clear them up (although first two at not at first glance obvious to me)?

quarto-mode.el:56:22: Warning: ‘make-variable-buffer-local’ not called at
    toplevel
quarto-mode.el:62:20: Warning: ‘make-variable-buffer-local’ not called at
    toplevel

In quarto-preview:
quarto-mode.el:217:11: Warning: Unused lexical variable `browser-path'

In quarto-mode--preview-refresh-complete:
quarto-mode.el:248:11: Warning: Unused lexical variable `data'
quarto-mode.el:248:25: Warning: Unused lexical variable `symbol-status'
quarto-mode.el:248:39: Warning: Unused lexical variable `error-thrown'

In quarto-mode--maybe-preview:
quarto-mode.el:261:13: Warning: Unused lexical variable
    `this-project-directory'

[cscheid]

Yes, we would appreciate further PRs! (Also note that I ran our melpazoid workflow and it failed for this PR. but for a strange reason in setup-python that I don't fully understand right now. My availability for this kind of work will unfortunately only be in a few weeks, but I will check in on this issue in the meantime.)