ci: Wrap failing pre-commit command

[aborgna-q]

pre-commit started failing to parse the cargo doc command;

cargo doc................................................................Failed
- hook id: cargo-doc
- exit code: 1

Executable `RUSTDOCFLAGS=-Dwarnings` not found

it may be related to a version update.

The solution, as we've done in other steps, is to wrap everything as a sh -c command.

[doug-q]

I snuck this change in in #1114. I thought I was helping, but here we are. Sorry about that.