Force string comparison of platform_release

Ideally this would use 'platform_version >= 6.2' (Windows 7 is version
6.1) but that, and 'platform_release != 7', cause InvalidVersion errors
with pip >= 24.1 (see pypa/packaging#774).

pyproject.toml

@@ -80,8 +80,8 @@ PyQt6-linux = [
   "PyQt6-WebEngine-Qt6 < 6.3;     python_version == '3.6.*'",
 ]
 PyQt6-windows = [
-  "PyQt6 >= 6.2; platform_release != '7'",
-  "PyQt6-WebEngine >= 6.2; platform_release != '7'",
+  "PyQt6 >= 6.2; platform_release not in '7'",
+  "PyQt6-WebEngine >= 6.2; platform_release not in '7'",
 ]
 PyQt6-darwin = [
   "PyQt6-Qt6 >= 6.2, != 6.6.1",
@@ -97,7 +97,7 @@ PySide6 = [
   "photini[PySide6-darwin]; platform_system == 'Darwin'",
 ]
 PySide6-linux = ["PySide6 >= 6.2"]
-PySide6-windows = ["PySide6 >= 6.2; platform_release != '7'"]
+PySide6-windows = ["PySide6 >= 6.2; platform_release not in '7'"]
 PySide6-darwin = ["PySide6 >= 6.2, != 6.6.1"]
 gpxpy = ["gpxpy >= 1.3.5, != 1.6.0"]
 Pillow = []