Performance regression (speed, alloc) in `string` and `Symbol` in Julia 1.12

With Julia 1.11.5 on a MacBook Pro M1:
```
julia> @b string(1)
15.014 ns (2 allocs: 56 bytes)

julia> @b Symbol("foo", 5)
127.793 ns (5 allocs: 176 bytes)
```

With Julia 1.12.0-beta3 on the same machine:
```
julia> @b string(1)
17.764 ns (2 allocs: 64 bytes)

julia> @b Symbol("foo", 5)
139.245 ns (7 allocs: 256 bytes)
```