You shouldn't manually update the
resolv.conf, because all changes will be overwritten by data that your local DHCP server provides. Therefore, the network manager of Raspbian Buster has configured by
/etc/dhcpcd.conf. Every configuration of this config file always is overwriting to other network config files on the OS.
All you need is that you should config your network by
/etc/dhcpcd.conf as you want. In this case, follow this procedure:
Then, add this line:
static domain_name_servers=126.96.36.199 188.8.131.52
Before Raspbian Strech (I'm not sure enough), you could do that. It's some difference we have here and you must follow them to configure the network.