don't try to use mock_dns on ruby 2.7

Author: jamis

.github/workflows/test.yml

@@ -3,7 +3,7 @@
 # the standalone one.
 
 name: Run Driver Tests
-on: #[push, pull_request]
+on: [ workflow_dispatch ]
 jobs:
   build:
     name: "${{matrix.os}} ruby-${{matrix.ruby}} mongodb-${{matrix.mongodb}} ${{matrix.topology}}"

spec/integration/reconnect_spec.rb

@@ -111,6 +111,8 @@
       # thread.kill should've similarly failed, but it doesn't.
       fails_on_jruby
 
+      minimum_mri_version '3.0.0'
+
       it 'recreates SRV monitor' do
         wait_for_discovery
 

spec/integration/srv_monitoring_spec.rb

@@ -76,6 +76,9 @@
     # NotImplementedError: recvmsg_nonblock is not implemented
     fails_on_jruby
 
+    # mock dns implementation doesn't play nice with 2.7, etc.
+    minimum_mri_version '3.0.0'
+
     around do |example|
       # Speed up the tests by listening on the fake ports we are using.
       done = false