debugger beta: Fix bug where debug Rust main running action failed (#31291)

@osiewicz @SomeoneToIgnore If you guys have time to look this over it
would be greatly appreciated. I wanted to move the bug fix into the task
resolution code but wasn't sure if there was a reason that we didn't
already.

The bug is caused by an env variable being empty when we send it as a
terminal command. When the shell resolves all the env variables there's
an extra space that gets added due to the empty env variable being
placed between two other variables.

Closes #31240

Release Notes:

- debugger beta: Fix a bug where debug main Rust runner action wouldn't
work

crates/debugger_ui/src/session/running.rs

@@ -874,6 +874,7 @@ impl RunningState {
                     args,
                     ..task.resolved.clone()
                 };
+
                 let terminal = project
                     .update_in(cx, |project, window, cx| {
                         project.create_terminal(
@@ -918,12 +919,6 @@ impl RunningState {
             };
 
             if config_is_valid {
-                // Ok(DebugTaskDefinition {
-                //     label,
-                //     adapter: DebugAdapterName(adapter),
-                //     config,
-                //     tcp_connection,
-                // })
             } else if let Some((task, locator_name)) = build_output {
                 let locator_name =
                     locator_name.context("Could not find a valid locator for a build task")?;
@@ -942,7 +937,7 @@ impl RunningState {
 
                 let scenario = dap_registry
                     .adapter(&adapter)
-                    .ok_or_else(|| anyhow!("{}: is not a valid adapter name", &adapter))
+                    .context(format!("{}: is not a valid adapter name", &adapter))
                     .map(|adapter| adapter.config_from_zed_format(zed_config))??;
                 config = scenario.config;
                 Self::substitute_variables_in_config(&mut config, &task_context);