testsuite: Simplify Python <3.5 fallback for TextIO

testsuite/driver/my_typing.py

@@ -24,8 +24,11 @@ except:
 # is taken. We exploit this below.
 
 # TextIO is missing on some older Pythons.
-if 'TextIO' in globals():
-    TextIO = typing.TextIO
+if 'TextIO' not in globals():
+    try:
+        TextIO = typing.TextIO
+    except ImportError:
+        TextIO = None # type: ignore
 else:
     TextIO = None # type: ignore