Update tblib to 2.0

docs/changes/old_py.removal

@@ -11,3 +11,5 @@ Related changes include:
 - ``setup.py`` no longer includes the ``setup_requires`` keyword.
   Installation with a tool that understands ``pyproject.toml`` is
   recommended.
+- The bundled tblib has been updated to version 2.0.
+- On Python 3.12b3, dumping tracebacks of greenlets is not available.

src/gevent/util.py

@@ -374,16 +374,42 @@ class GreenletTree(object):
     @staticmethod
     def __render_tb(tree, label, frame, limit):
         tree.child_data(label)
-        # XXX: Issues with tblib?
-        # 3.12b3 is crashing walking the stack on macOS;
-        # on Linux CI, it is failing with a nice attribute error
+        # XXX: Issues with tblib? Seen with tblib 1.3 and 2.0.
+        # More likely, it's something wrong in greenlet and the way it's
+        # keeping track of the frames?
+        #
+        # In a test like this:
+        #
+        #   g = gevent.spawn(util.print_run_info, file=io)
+        #   g.join() (test__util.py, line 53)
+        #
+        # 3.12b3 is crashing walking the stack on macOS:
+        # It's a simple segfault on line 340, ``f = f.f_back``.
+        # I have confirmed that the object is a real frame object.
+        #
+        # It seems unlikely to be a greenlet thing though, because the frame we're
+        # crashing on is the root frame:
+        #
+        # <frame at 0x.., file '/gevent/tests/test__util.py', line 53, code root>
+        #
+        # Interestingly, we see the test case dump the stack of the greenlet (successfully),
+        # then dump the stack of the main thread (successfully) --- this ends in line 53 --,
+        # and then get _another_ frame for line 53, and this is where it crashes.
+        # The difference? The successful dump does not list it as a root frame,
+        # where the failed one does.
+        #
+        #
+        # on Linux CI (not sure what frame), it is failing with a nice attribute error
         # (which watches where the macOS is failing, inside a call to
         # Py_GetAttr):
         #
-        # File "/opt/hostedtoolcache/Python/3.12.0-beta.3/x64/lib/python3.12/traceback.py", line 339, in walk_stack
+        # File "//python3.12/traceback.py", line 339, in walk_stack
         #   yield f, f.f_lineno
         # AttributeError: 'dict' object has no attribute 'f_lineno'
-
+        #
+        # A workaround on macOS is to not dump the root frame, but that only fixes
+        # test__util. test__threadpool:test_greenlet_class crashes similarly, but
+        # not 100% of the time.
         if sys.version_info != (3, 12, 0, 'beta', 3):
             tb = ''.join(traceback.format_stack(frame, limit))
         else: