fix: re-export ExceptionGroup for now (#1164)

* fix: re-export ExceptionGroup for now

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* Update src/packaging/metadata.py

---------

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

Author: henryiii

src/packaging/metadata.py

@@ -27,6 +27,7 @@
 
 
 __all__ = [
+    "ExceptionGroup",  # Keep this for a bit (makes mypy happy w/ 26.0 compat)
     "InvalidMetadata",
     "Metadata",
     "RFC822Message",