Allow use of wasip3 0.3 for MSRV reasons.

This allows a project dependeing on `getrandom` to use this to get
an Fully Rust-1.85-compatible Cargo.lock, while still allowing projects
with newer MSRV to use 0.4:

```
CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS=fallback cargo update -p getrandom
```

Inspired by the windows-sys documentation that recommends using the same
pattern.

Author: briansmith

Cargo.toml

@@ -82,7 +82,12 @@ wasip2 = { version = "1", default-features = false }
 
 # wasi_p2_3
 [target.'cfg(all(target_arch = "wasm32", target_os = "wasi", target_env = "p3"))'.dependencies]
-wasip3 = "0.4"
+# TODO(MSRV): Remove 0.3.
+# Projects that need to support MSRV 1.85 can use the following:
+# ```
+# CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS=fallback cargo update -p getrandom
+# ```
+wasip3 = ">=0.3, <=0.4"
 
 # wasm_js
 [target.'cfg(all(target_arch = "wasm32", any(target_os = "unknown", target_os = "none")))'.dependencies]