Updates to pr labeling workflow

[Firgrep]

To mark as content:

• .md files
• cspell.json file lying at root
• .bib files

We'll add to this list as we discover more and sort it out in a batch.

[Firgrep]

Perhaps add _meta.ts and _meta.tsx files (but only those, not other .ts or .tsx files) to content

[Firgrep]

Did some small update. Dealing with named files (and not just extensions) requires a larger rewrite, so I'll leave that for later for whoever wants to grab it :)