scripts: Do not hard-code /bin/bash.

Instead, use Bash from PATH.  This approach works more reliably on
distributions not strictly adhering to the File Hierarchy
Standard (FHS) such as Guix System or NixOS.

Change-Id: Ic7b168d0f4d73f3a1cb1085e9a84600a25d153c5

scripts/format.sh

@@ -51,7 +51,7 @@ install_hook()
         exit 1
     fi
     echo Installing pre-commit hook in "$hooks_path"
-    echo "/bin/bash $(realpath $0)" > "$hooks_path"/pre-commit
+    echo "$(realpath $0)" > "$hooks_path"/pre-commit
     chmod +x "$hooks_path"/pre-commit
 }