rust: Add runnable icon for #[cfg(test)] mod tests (#12017)

This allows you to run all the tests inside the `mod tests` block. 
Fixes #11967.

<img width="366" alt="Screenshot 2024-05-18 at 16 07 32"
src="https://github.com/zed-industries/zed/assets/62463826/01fc378c-1546-421d-8250-fe0227c1e5a0">

<img width="874" alt="Screenshot 2024-05-18 at 16 37 21"
src="https://github.com/zed-industries/zed/assets/62463826/4a880b91-df84-4917-a16e-5d5fe20e22ac">

Release Notes:

- Added runnable icon for Rust `#[cfg(test)] mod tests` blocks
([#11967](https://github.com/zed-industries/zed/issues/11967)).

crates/languages/src/rust.rs

@@ -389,6 +389,22 @@ impl ContextProvider for RustContextProvider {
                 tags: vec!["rust-test".to_owned()],
                 ..TaskTemplate::default()
             },
+            TaskTemplate {
+                label: format!(
+                    "cargo test -p {} {}",
+                    RUST_PACKAGE_TASK_VARIABLE.template_value(),
+                    VariableName::Stem.template_value(),
+                ),
+                command: "cargo".into(),
+                args: vec![
+                    "test".into(),
+                    "-p".into(),
+                    RUST_PACKAGE_TASK_VARIABLE.template_value(),
+                    VariableName::Stem.template_value(),
+                ],
+                tags: vec!["rust-mod-test".to_owned()],
+                ..TaskTemplate::default()
+            },
             TaskTemplate {
                 label: format!(
                     "cargo test -p {}",