`verify_output()` issue with constructed calls

[lionel-]

It seems it deparses calls with expr_print() and then tries to reparse these. Verifying the output of vars_pull(vars, !!c("a", "b")) creates this output file:

vars_pull(vars, <chr: "a", "b">)
Error: <text>:11:17: unexpected '<'
10: vars_pull(letters, "foo")
11: vars_pull(vars, <

[lionel-]

Probably we can use substitute() instead of enquo(), which will also make verify_output() more useful with tidyeval functions (better timing of unquoting).