(very minor): etable TeX fixef size row contains unsanitized `#`, which breaks latex compilation

[apoorvalal]

Noticed a very minor issue that I didn't think would be worth opening a PR for (I fixed it in my fork but want to install your new goodies, so want to get merged in master).

This line

fixest/R/etable.R

Line 3959 in d8334bd

fixef_sizes.prefix = "# ", fixef_sizes.suffix = "",

and 10 lines below it
adds an unsanitized # to the tex export from etable, which in turn breaks compilation. Just needs to be escaped with "\" to fix.

[lrberge]

Thanks! I don't know when I introduced the bug since it was working at some point.... I think before I was escaping ex post but I changed that later on.
Anyway, now corrected!