DNS settings can't be changed by non-admin user as of 10.15.5

[cboone]

Same problem as jedisct1/bitbar-dnscrypt-proxy-switcher/issues/5.

networksetup behavior now depends on the type of user running it:

networksetup Command
Starting with macOS 10.15.5, the networksetup command behaves differently when run as a standard user versus an admin user. Standard users can do the following:
• 1. Read various network settings
• 2. Turn Wi-Fi power on or off (networksetup -setairportpower en0 on)
• 3. Change the Wi-Fi access point (networksetup -setairportnetwork en0
ExampleWiFiAP)
Other network settings can no longer be modified by standard users via networksetup.
For admin users, networksetup will continue to behave as it has in previous releases of macOS, provided System Preferences > Security & Privacy > Advanced… > “Require an administrator password to access system-wide preferences” is unchecked (which is the default state). If it is checked, admins will be bound by the same constraints as standard users when
using networksetup.

https://mrmacintosh.com/whats-new-in-the-macos-catalina-10-15-5-update-19f96/

To get mine working, I prepended sudo onto the networksetup -setdnsservers call and set up sudoers to allow my non-admin user to run networksetup, as described here. But that's not optimal (due to needing to edit sudoers) and isn't a general fix.