Simplify the code, using into_encoded_bytes

It used `as_encoded_bytes` before, which required more other steps.

Both functions require Rust 1.74, so the MSRVC for `gix-command`,
whih is 1.70, will not support them. That remains to be resolved.

Author: EliahKagan

gix-command/tests/command.rs

@@ -567,12 +567,11 @@ mod spawn {
         use gix_testtools::bstr::{BString, ByteSlice, ByteVec};
 
         fn script_path(filename: impl AsRef<Path>) -> crate::Result<OsString> {
-            let native_path = gix_testtools::scripted_fixture_read_only("scripts.sh")?
+            let native_path: BString = gix_testtools::scripted_fixture_read_only("scripts.sh")?
                 .join(filename)
-                .as_os_str()
-                .as_encoded_bytes()
-                .as_bstr()
-                .to_owned();
+                .into_os_string()
+                .into_encoded_bytes()
+                .into();
             let unix_path = gix_path::to_unix_separators_on_windows(native_path)
                 .to_os_str()?
                 .to_owned();