glue symbol extraction should treat x and `` `x` `` the same

_Originally posted by @AshesITR in https://github.com/r-lib/lintr/pull/1612#discussion_r987609552_

```r
x <- 1
`x` <- 2
glue::glue("{x} is the same as {`x`}")
# 2 is the same as 2
```