Correct set vs. frozenset unmarshal code type

Also, don't isort tests.
Add a source code for a test that we have bytecode for.

Author: rocky

.pre-commit-config.yaml

@@ -8,10 +8,11 @@ repos:
     - id: debug-statements
       stages: [pre-commit]
     - id: end-of-file-fixer
-      exclude: '^pytest/testdata'
+      exclude: '^pytest/testdata|^test/simple_source'
       stages: [pre-commit]
 -   repo: https://github.com/pycqa/isort
     rev: 5.13.2
     hooks:
       - id: isort
+        exclude: '^pytest/testdata|^test/simple_source'
         stages: [pre-commit]

test/simple_source/expression/06_frozenset.py

@@ -0,0 +1,5 @@
+# Bug from Python 3.3 _markupbase.py cross compilatin
+# error in unmarshaling a frozenset
+import sys
+if sys.argv[0] in frozenset({"attlist", "linktype", "link", "element"}):
+    print("Yep")

xdis/unmarshal.py

@@ -83,8 +83,8 @@ def long(n: int) -> LongTypeForPython3:
     ")": "small_tuple",
     "(": "tuple",
     "[": "list",
-    "<": "frozenset",
-    ">": "set",
+    "<": "set",
+    ">": "frozenset",
     "{": "dict",
     "R": "python2_string_reference",
     "c": "code",