[R] Argument names ignored in schema supplied as `in_type` argument to `register_scalar_function()`

### Describe the bug, including details regarding any error messages, version, and platform.

For `in_type`, I would have expected the argument name should match the data. But this doesn't seem to be the case

```
library(arrow)
library(dplyr)
# Make data set
write.csv(sleep, "sleep.csv", row.names = F)

# Register function
register_scalar_function(
name = "f",
fun = function(context, x) as.integer(x),
in_type = schema(blah = int64()), # NOTE: Schema name
out_type = int32(),
auto_convert = TRUE
)

open_dataset("sleep.csv", format = "csv") |>
mutate(f(group)) |>
head() |>
collect()

```

### Component(s)

R