feat: Look for bash in (git root)/bin, then (git root)/usr/bin

This changes `bash_program()` so that it will find the `bash.exe`
provided by Git for Windows that is most reliable for our use in
runinng test fixture scripts, of those that are available. First
it uses the shim, but falls back to the non-shim if the shim is
not available. If neither is found, then the fallback of using the
simple command `bash.exe` (which triggers a path search when run)
continues to be used.

Author: EliahKagan

tests/tools/src/lib.rs

@@ -653,21 +653,25 @@ fn configure_command<'a, I: IntoIterator<Item = S>, S: AsRef<OsStr>>(
 }
 
 fn bash_program() -> &'static Path {
-    // TODO(deps): *Maybe* add something to `gix-path` like `env::shell()` that can be used to
-    //             find bash and, once the version `gix-testtools` depends on has it, use it.
+    // TODO(deps): Unify with `gix_path::env::shell()` by having both call a more general function
+    //             in `gix-path`. See https://github.com/GitoxideLabs/gitoxide/issues/1886.
     static GIT_BASH: Lazy<PathBuf> = Lazy::new(|| {
         if cfg!(windows) {
             GIT_CORE_DIR
                 .ancestors()
                 .nth(3)
-                .map(OsString::from)
-                .map(|mut raw_path| {
-                    // Go down to where `bash.exe` usually is. Keep using `/` separators (not `\`).
-                    raw_path.push("/usr/bin/bash.exe");
-                    raw_path
+                .map(OsStr::new)
+                .iter()
+                .flat_map(|prefix| {
+                    // Go down to places `bash.exe` usually is. Keep using `/` separators, not `\`.
+                    ["/bin/bash.exe", "/usr/bin/bash.exe"].into_iter().map(|suffix| {
+                        let mut raw_path = (*prefix).to_owned();
+                        raw_path.push(suffix);
+                        raw_path
+                    })
                 })
                 .map(PathBuf::from)
-                .filter(|bash| bash.is_file())
+                .find(|bash| bash.is_file())
                 .unwrap_or_else(|| "bash.exe".into())
         } else {
             "bash".into()