disable dnsclient because it is fragile

[ringabout]

  Unhandled exception: /home/runner/work/Nim/Nim/pkgstemp/dnsclient/tests/test1.nim(28, 3) `rr.strings == @["dnsclient.nim"]`  [AssertionDefect]
  [FAILED] query TXT
  [OK] query MX
  [OK] query CNAME
  [OK] query SRV
  Error: execution of an external program failed: '/home/runner/work/Nim/Nim/pkgstemp/dnsclient/tests/test1'
         Tip: 2 messages have been suppressed, use --verbose to show them.
  tools.nim(36)            doCmd
  
      Error:  Execution failed with exit code 1
          ... Command: /home/runner/work/Nim/Nim/bin/nim c --noNimblePath -d:NimblePkgVersion=0.3.4 --hints:off -r --path:. /home/runner/work/Nim/Nim/pkgstemp/dnsclient/tests/test1 

[ringabout]

It sends queries to http:https://txt.example.huy.im/, which is quite suspious

test "query TXT":
  let resp = client.sendQuery("txt.example.huy.im", TXT)
  assert resp.answers[0].kind == TXT
  let rr = TXTRecord(resp.answers[0])
  assert rr.strings == @["dnsclient.nim"]

[ringabout]

cc @ba0f3

[github-actions]

Thanks for your hard work on this PR!
The lines below are statistics of the Nim compiler built from c58b6e8

Hint: mm: orc; opt: speed; options: -d:release
178820 lines; 8.336s; 664.246MiB peakmem

[ba0f3]

It sends queries to http:https://txt.example.huy.im/, which is quite suspious

test "query TXT":
  let resp = client.sendQuery("txt.example.huy.im", TXT)
  assert resp.answers[0].kind == TXT
  let rr = TXTRecord(resp.answers[0])
  assert rr.strings == @["dnsclient.nim"]

it does not send http request to http:https://txt.example.huy.im/, it asked for TXT record txt.example.huy.im via DNS protocol