py*-dnspython conflicts with py*-py3dns on case-insensitive OS

[barracuda156]

One port installs into site-packages/dns and another into site-packages/DNS.

So, for example, when I tried to install py311-dnspython after installing py311-py3dns, it resulted in an error:

Error: Failed to activate py311-dnspython: Image error: /opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/dns/__init__.py already exists and does not belong to a registered port.  Unable to activate port py311-dnspython. Use 'port -f activate py311-dnspython' to force the activation.
    while executing
"throw registry::image-error $msg"
    ("foreach" body line 50)
    invoked from within
"foreach file $imagefiles {
                set srcfile "${extracted_dir}${file}"

                # To be able to install links, we test if we can lst..."
    invoked from within
"registry::write {
            foreach file $imagefiles {
                set srcfile "${extracted_dir}${file}"

                # To be able to instal..."