TEST: add the output to the new with-env example (#8148)

Related to #8119.
Should address the review comment by @sholderbach from #8119.


# Description

this PR adds the output to the new example for the `with-env` command
introduced by #8119.

```bash
with-env {X: "Y", W: "Z"} { [$env.X $env.W] }
```
should output
```bash
["Y", "Z"]
```
hence the proposition from @sholderbach, i.e.
```rust
Some(Value::list(
    vec![Value::test_string("Y"), Value::test_string("Z")],
    Span::test_data(),
))
```

# User-Facing Changes
_none_

# Tests + Formatting

not really a test, only the output value for the last `with-env` example

- ✔️ `cargo fmt --all`
- ✔️ `cargo clippy --workspace -- -D warnings -D
clippy::unwrap_used -A clippy::needless_collect`
- ✔️ `cargo test --workspace`

# After Submitting
_none_

crates/nu-command/src/env/with_env.rs

@@ -4,7 +4,7 @@ use nu_engine::{eval_block, CallExt};
 use nu_protocol::{
     ast::Call,
     engine::{Closure, Command, EngineState, Stack},
-    Category, Example, PipelineData, ShellError, Signature, SyntaxShape, Type, Value,
+    Category, Example, PipelineData, ShellError, Signature, Span, SyntaxShape, Type, Value,
 };
 
 #[derive(Clone)]
@@ -65,7 +65,10 @@ impl Command for WithEnv {
             Example {
                 description: "Set by key-value record",
                 example: r#"with-env {X: "Y", W: "Z"} { [$env.X $env.W] }"#,
-                result: None,
+                result: Some(Value::list(
+                    vec![Value::test_string("Y"), Value::test_string("Z")],
+                    Span::test_data(),
+                )),
             },
         ]
     }