expect_snapshot() fails when names contain backquotes

[moodymudskipper]

When running such test:

test_that("backquotes", {
  expect_snapshot(
    c("`a`" = 1)
  )
})

I get :

`c(`\`a\`` = 2)` threw an unexpected error.
Message: attempt to use zero-length variable name
Class:   simpleError/error/condition

[hadley]

This looks like an rlang bug: r-lib/rlang#1642

However maybe we should just use deparse() instead of expr_deparse().