fix windows clippy

[bw-solana]

Problem

Seeing CI failures:

error: manually constructing a nul-terminated string
   --> install\src\command.rs:427:17
    |
427 |                 "Environment\0".as_ptr() as LPARAM,
    |                 ^^^^^^^^^^^^^^^ help: use a `c""` literal: `c"Environment"`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_c_str_literals
    = note: `-D clippy::manual-c-str-literals` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::manual_c_str_literals)]`

error: could not compile `agave-install` (lib) due to 1 previous error

Summary of Changes

Switch to using c literal