don't expand tilde if we quote external arguments (#7711)

# Description

As title
Fixes: #7673
Fixes: #4205
Also possiblely fixes: https://github.com/nushell/nushell/issues/6993

# User-Facing Changes

Before:
```
> ^echo "~"
/Users/ttt
```

After:
```
> ^echo "~"
~
```
# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/src/system/run_external.rs

@@ -600,9 +600,11 @@ impl ExternalCommand {
                 span: arg.span,
             };
 
-            arg.item = nu_path::expand_tilde(arg.item)
-                .to_string_lossy()
-                .to_string();
+            if !keep_raw {
+                arg.item = nu_path::expand_tilde(arg.item)
+                    .to_string_lossy()
+                    .to_string();
+            }
 
             let cwd = PathBuf::from(cwd);