Merge Python 3.8+ tests into main test modules

Now that we require Python 3.8 or later, we don't need to separate
Python 3.8+ tests into their own modules.

testsuite/N805.py

@@ -179,3 +179,11 @@ class ButWeLostTheOriginalStaticMethodLateDecorator:
     async def test(so, exciting):
         pass
     test = staticmethod(test)
+#: Okay
+class C:
+    def __init__(self, a, /, b=None):
+        pass
+#: N805:2:18
+class C:
+    def __init__(this, a, /, b=None):
+        pass

testsuite/N806.py

@@ -222,3 +222,21 @@ async def test():
 async def f():
     async with expr as ASYNC_VAR:
         pass
+#: Okay
+def f1(values):
+    total = 0
+    partial_sums = [total := total + v for v in values]
+    return partial_sums, total
+#: Okay
+GLOBAL_VAR = 0
+def f2(values):
+    global GLOBAL_VAR
+    partial_sums = [GLOBAL_VAR := GLOBAL_VAR + v for v in values]
+    return partial_sums, GLOBAL_VAR
+#: N806:2:16
+def f():
+    return 1, (BaD_WalRuS := 1), BaD_WalRuS + 1
+#: Okay
+def f():
+    (NamedTuple := namedtuple('NamedTuple', 'f1 f2'))
+    return NamedTuple

testsuite/N816.py

@@ -53,3 +53,7 @@
 #: N816
 async for γΓ1 in iterator:
     pass
+#: Okay
+lambda f: (TheName := namedtuple('TheName', 'a b c')), TheName
+#: N816:1:15:
+lambda line: (BaD_WaLRuS := re.match(pattern, line)) and BaD_WaLRuS.group(1)