Make types compatible with Python 3.9 and 3.10

Signed-off-by: Joe Friedrichsen <114173023+jfriedri-ni@users.noreply.github.com>

Author: jfriedri-ni

examples/placeholder.py

@@ -21,8 +21,8 @@ class MyIntEnum(enum.IntEnum):
     VALUE30 = 30
 
 
-class MyStrEnum(enum.StrEnum):
-    """Example of a StrEnum enum."""
+class MyStrEnum(str, enum.Enum):
+    """Example of a mixin string enum."""
 
     VALUE1 = "value1"
     VALUE2 = "value2"

tests/types.py

@@ -1,6 +1,16 @@
 """Types that exercise conversion to and from protobuf."""
 
 import enum
+import sys
+
+if sys.version_info >= (3, 11):
+    from enum import StrEnum
+else:
+
+    class StrEnum(str, enum.Enum):
+        """Example of a mixin string enum."""
+
+        pass
 
 
 class MyIntFlags(enum.IntFlag):
@@ -27,7 +37,7 @@ class MixinIntEnum(int, enum.Enum):
     VALUE33 = 33
 
 
-class MyStrEnum(enum.StrEnum):
+class MyStrEnum(StrEnum):
     """Example of a StrEnum enum."""
 
     VALUE1 = "value1"