Filter region coordinate spinboxes can't be modified when automatic filter region enabled

Steps to reproduce:

• open Inkscape
• create a rectangle
• add a blur (can be done via the Fill and stroke dialog)
• open the filter effects dialogs
• switch to the Filter General settings (at the bottom of the dialog)
• options are all enabled
• try to change the coordinates

What happened?

• you can't change the Coordinates/Dimensions without disabling Automatic region

What should have happened?

• either changing them automatically disables the Automatic region option
• or if automatic region is checked, the other options should not be sensitive (so you can't modify values)

Version Info:

• Inkscape 1.1-dev (e50f85a1, 2020-12-17) Linux Mint 20
• so I don't have to look later, automatic filter region added in !2430 (merged)