Detection of PEP 604 union syntax.

### Description

Fixes #8478

Handle `UnionType` as arguments to `Mapped`, e.g., `Mapped[str | None]`:

- adds `utils.typing.is_optional_union()` used to detect if a column should be nullable.
- adds `"UnionType"` to `utils.typing.is_optional()` names.
- uses `get_origin()` in `utils.typing.is_origin_of()` as `UnionType` has no `__origin__` attribute.
- tests with runtime type and postponed annotations and guard the tests running with `compat.py310`.

### Checklist
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This pull request is:

- [ ] A documentation / typographical error fix
	- Good to go, no issue or tests are needed
- [x] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

**Have a nice day!**

Closes: #8479
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/8479
Pull-request-sha: 12417654822272c5847e684c53677f665553ef0e

Change-Id: Ib3248043dd4a97324ac592c048385006536b2d49

2 files changed, 11 insertions, 8 deletions

diff --git a/lib/sqlalchemy/orm/properties.py b/lib/sqlalchemy/orm/properties.py
index 6213cfef8..7d7175678 100644
--- a/lib/sqlalchemy/orm/properties.py
+++ b/lib/sqlalchemy/orm/properties.py
@@ -52,8 +52,8 @@ from ..sql.schema import SchemaConst
 from ..util.typing import de_optionalize_union_types
 from ..util.typing import de_stringify_annotation
 from ..util.typing import is_fwd_ref
+from ..util.typing import is_optional_union
 from ..util.typing import is_pep593
-from ..util.typing import NoneType
 from ..util.typing import Self
 from ..util.typing import typing_get_args
 
@@ -652,17 +652,15 @@ class MappedColumn(
     ) -> None:
         sqltype = self.column.type
 
-        nullable = False
+        if is_fwd_ref(argument):
+            argument = de_stringify_annotation(cls, argument)
 
-        if hasattr(argument, "__origin__"):
-            nullable = NoneType in argument.__args__  # type: ignore
+        nullable = is_optional_union(argument)
 
         if not self._has_nullable:
             self.column.nullable = nullable
 
         our_type = de_optionalize_union_types(argument)
-        if is_fwd_ref(our_type):
-            our_type = de_stringify_annotation(cls, our_type)
 
         use_args_from = None
         if is_pep593(our_type):
diff --git a/lib/sqlalchemy/util/typing.py b/lib/sqlalchemy/util/typing.py
index 45fe63765..85c1bae72 100644
--- a/lib/sqlalchemy/util/typing.py
+++ b/lib/sqlalchemy/util/typing.py
@@ -169,7 +169,7 @@ def make_union_type(*types: _AnnotationScanType) -> Type[Any]:
 def expand_unions(
     type_: Type[Any], include_union: bool = False, discard_none: bool = False
 ) -> Tuple[Type[Any], ...]:
-    """Return a type as as a tuple of individual types, expanding for
+    """Return a type as a tuple of individual types, expanding for
     ``Union`` types."""
 
     if is_union(type_):
@@ -191,9 +191,14 @@ def is_optional(type_):
         type_,
         "Optional",
         "Union",
+        "UnionType",
     )
 
 
+def is_optional_union(type_: Any) -> bool:
+    return is_optional(type_) and NoneType in typing_get_args(type_)
+
+
 def is_union(type_):
     return is_origin_of(type_, "Union")
 
@@ -204,7 +209,7 @@ def is_origin_of(
     """return True if the given type has an __origin__ with the given name
     and optional module."""
 
-    origin = getattr(type_, "__origin__", None)
+    origin = typing_get_origin(type_)
     if origin is None:
         return False