Inconsistent formatting when interpolating into `.code`

```r
# Expected output
cli::format_inline("{.code foo = bar}")
#> [1] "`foo = bar`"

x <- "foo"
y <- "bar"

# Output with CRAN cli
cli::format_inline("{.code {x} = {y}}")
#> [1] "`` `foo` = `bar` ``"

# Output with dev cli
cli::format_inline("{.code {x} = {y}}")
#> [1] "`foo` = `bar`"

```