fix: make task failure errors include stack of running tasks (#2286)

Previously if a task was run as a dependency of another task,
the error message simply reported something like:

    exit status 1

It is desirable instead to name the root task and all child tasks in the tree
to the failing task.

After this PR, the error message will read:

    task: Failed to run task "root": task: Failed to run task "failing-task": exit status 1

executor_test.go

@@ -665,6 +665,15 @@ func TestLabel(t *testing.T) {
 		),
 		WithTask("foo"),
 	)
+
+	NewExecutorTest(t,
+		WithName("label in error"),
+		WithExecutorOptions(
+			task.WithDir("testdata/label_error"),
+		),
+		WithTask("foo"),
+		WithRunError(),
+	)
 }
 
 func TestPromptInSummary(t *testing.T) {