find where deprecation warnings come from

[maelle]

@krlmlr could you please copy-paste them here?

[krlmlr]

── 4. User Action Items ───────────────────────────────────────────────────────────
• Run `devtools::check_win_devel()`.
• Run `rhub::check_for_cran()`.
• Run `urlchecker::url_update()`.
• Check all items in cran-comments.md.
• Convert NEWS.md from changelog format to release notes.
• Run `fledge::release()`.
Warning messages:
1: `as_integer()` is deprecated as of rlang 0.4.0
Please use `vctrs::vec_cast()` instead.
This warning is displayed once every 8 hours. 
2: `as_character()` is deprecated as of rlang 0.4.0
Please use `vctrs::vec_cast()` instead.
This warning is displayed once every 8 hours. 
3: `as_logical()` is deprecated as of rlang 0.4.0
Please use `vctrs::vec_cast()` instead.
This warning is displayed once every 8 hours. 

I believe this will be easier to tackle after #658 -- if it's in cran_prepare() it will be easier to iterate.

[maelle]

@krlmlr are you still getting them?