fix: change :: to =

Author: BobTheBuidler

mypyc/test-data/irbuild-classes.test

@@ -2891,9 +2891,9 @@ def isinstance_nonnative(x):
 L0:
     r0 = __main__.NonNative :: type
     r1 = get_element_ptr x ob_type :: PyObject
-    r2 :: borrow load_mem r1 :: builtins.object*
+    r2 = borrow load_mem r1 :: builtins.object*
     keep_alive x
-    r3 :: r2 == r0
+    r3 = r2 == r0
     return r3
 def isinstance_interpreted_subclasses(x):
     x, r0 :: object