gh-116767: fix crash on 'async with' with many context managers (GH-118348)

Account for `add_stopiteration_handler` pushing a block for `async with`.
To allow generator functions that previously almost hit the `CO_MAXBLOCKS`
limit by nesting non-async blocks, the limit is increased by 1.
This increase allows one more block in non-generator functions.

Lib/test/test_syntax.py

@@ -2392,13 +2392,40 @@ if x:
             code += "): yield a"
             return code
 
-        CO_MAXBLOCKS = 20  # static nesting limit of the compiler
+        CO_MAXBLOCKS = 21  # static nesting limit of the compiler
+        MAX_MANAGERS = CO_MAXBLOCKS - 1  # One for the StopIteration block
 
-        for n in range(CO_MAXBLOCKS):
+        for n in range(MAX_MANAGERS):
             with self.subTest(f"within range: {n=}"):
                 compile(get_code(n), "<string>", "exec")
 
-        for n in range(CO_MAXBLOCKS, CO_MAXBLOCKS + 5):
+        for n in range(MAX_MANAGERS, MAX_MANAGERS + 5):
+            with self.subTest(f"out of range: {n=}"):
+                self._check_error(get_code(n), "too many statically nested blocks")
+
+    @support.cpython_only
+    def test_async_with_statement_many_context_managers(self):
+        # See gh-116767
+
+        def get_code(n):
+            code = [ textwrap.dedent("""
+                async def bug():
+                    async with (
+                    a
+                """) ]
+            for i in range(n):
+                code.append(f"    as a{i}, a\n")
+            code.append("): yield a")
+            return "".join(code)
+
+        CO_MAXBLOCKS = 21  # static nesting limit of the compiler
+        MAX_MANAGERS = CO_MAXBLOCKS - 1  # One for the StopIteration block
+
+        for n in range(MAX_MANAGERS):
+            with self.subTest(f"within range: {n=}"):
+                compile(get_code(n), "<string>", "exec")
+
+        for n in range(MAX_MANAGERS, MAX_MANAGERS + 5):
             with self.subTest(f"out of range: {n=}"):
                 self._check_error(get_code(n), "too many statically nested blocks")
 
@@ -2536,7 +2563,8 @@ while 1:
                   while 20:
                    while 21:
                     while 22:
-                     break
+                     while 23:
+                      break
 """
         self._check_error(source, "too many statically nested blocks")