nixos/test-driver: improve wording on comments about new error handling

Co-authored-by: Benoit de Chezelles <bew@users.noreply.github.com>

nixos/lib/test-driver/src/test_driver/driver.py

@@ -188,6 +188,8 @@ class Driver:
                 sys.exit(1)
             except RequestedAssertionFailed:
                 exc_type, exc, tb = sys.exc_info()
+                # We manually print the stack frames, keeping only the ones from the test script
+                # (note: because the script is not a real file, the frame filename is `<string>`)
                 filtered = [
                     frame
                     for frame in traceback.extract_tb(tb)

nixos/lib/test-driver/src/test_driver/errors.py

@@ -15,6 +15,6 @@ class RequestedAssertionFailed(AssertionError):
     e.g. a failing `t.assertEqual(...)` or `machine.succeed(...)`.
 
     This gets special treatment in error reporting: i.e. it gets
-    `!!!` as prefix just as `MachineError`, but all stack frames that are
-    not from `testScript` also get removed.
+    `!!!` as prefix just as `MachineError`, but only stack frames coming
+    from `testScript` will show up in logs.
     """