Update dependencies

This adds 'all' to install every optional dependency and fixes a
problem installing PyQt6 with Python 3.6.

pyproject.toml

@@ -55,13 +55,19 @@ importer = ["gphoto2 >= 1.8; platform_system != 'Windows'"]
 ipernity = ["photini[keyring,requests-toolbelt]"]
 pixelfed = ["photini[keyring,requests-oauthlib,requests-toolbelt]"]
 spelling = ["pyenchant >= 2.0"]
+# install everything except the Qt package
+all = ["""photini[keyring,requests-oauthlib,requests-toolbelt,\
+importer,spelling,gpxpy,Pillow]"""]
 # set versions of common packages
 keyring = ["keyring >= 7.0"]
 requests-oauthlib = ["requests-oauthlib >= 1.0"]
 requests-toolbelt = ["requests-toolbelt >= 0.9"]
 # the following are intended for use by the photini-configure script
 PyQt5 = ["PyQt5 >= 5.9", "PyQtWebEngine >= 5.12"]
-PyQt6 = ["PyQt6 >= 6.2", "PyQt6-WebEngine >= 6.2"]
+PyQt6 = ["PyQt6 >= 6.2", "PyQt6-WebEngine >= 6.2",
+  "PyQt6-Qt6 < 6.3; python_version == '3.6.*'",
+  "PyQt6-WebEngine-Qt6 < 6.3; python_version == '3.6.*'"
+]
 PySide2 = ["PySide2 >= 5.11"]
 PySide6 = ["PySide6 >= 6.2"]
 gpxpy = ["gpxpy >= 1.3.5"]