Merge #20288: script, doc: contrib/seeds updates

961f148cb1 doc: update contrib/seeds/README dnspython installation info (Jon Atack)
dd7b5f46d8 script: fix deprecation warning in makeseeds.py (Jon Atack)

Pull request description:

  Seen while reviewing #20237.

  1. Fix a deprecation warning in `contrib/seeds/makeseeds.py`
  ```
      makeseeds.py:139: DeprecationWarning: please use dns.resolver.resolve() instead
        asn = int([x.to_text() for x in dns.resolver.query('.'.join(
  ```
    - Per https://dnspython.readthedocs.io/en/latest/whatsnew.html, `dns.resolver.query()` was deprecated in `dnspython` version 2.0.0.

    - See https://dnspython.readthedocs.io/en/latest/resolver-class.html for more info on the resolver class.

  2. Update the `dnspython` dependency installation instructions in `contrib/seeds/README`

    - The markdown rendering can be seen here: https://github.com/jonatack/bitcoin/tree/contrib-seeds-fixups/contrib/seeds

ACKs for top commit:
  laanwj:
    code review ACK 961f148cb1

Tree-SHA512: f9c4f318a1a0d35b8de147d24b72c534a1f58eece31e7cfa00b4149a63b6a618d8ca0312f52fd8056f3c645cf2ee68574ca02319fddffdad919a70cd33395d33

contrib/seeds/README.md

@@ -16,6 +16,12 @@ The seeds compiled into the release are created from sipa's DNS seed data, like
 
 ## Dependencies
 
-Ubuntu:
+Ubuntu, Debian:
 
     sudo apt-get install python3-dnspython
+
+and/or for other operating systems:
+
+    pip install dnspython
+
+See https://dnspython.readthedocs.io/en/latest/installation.html for more information.

contrib/seeds/makeseeds.py

@@ -136,7 +136,7 @@ def lookup_asn(net, ip):
             ipaddr = res.rstrip('.')            # 2.0.0.1.4.8.6.0.b.0.0.2.0.0.2.3
             prefix = '.origin6'
 
-        asn = int([x.to_text() for x in dns.resolver.query('.'.join(
+        asn = int([x.to_text() for x in dns.resolver.resolve('.'.join(
                    reversed(ipaddr.split('.'))) + prefix + '.asn.cymru.com',
                    'TXT').response.answer][0].split('\"')[1].split(' ')[0])
         return asn