github: Fix up malformed /etc/hosts.

For some reason /etc/hosts in GHA now contains a plain text line
like this:

  Note: Don't Delete this file. Also, don't remove this line. ...

This breaks libunbound and makes a series of unit tests to emit
following warning:
  |00001|dns_resolve|WARN|Failed to read etc/hosts: syntax error

Working around this issue by removing a bad line from /etc/hosts
until this fixed properly by GitHub team.  This in combination
with other fixes should unblock CI.

Bug for virtual-environments:
  actions/runner-images#3353

Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Reviewed-by: David Marchand <david.marchand@redhat.com>

.github/workflows/build-and-test.yml

@@ -113,6 +113,12 @@ jobs:
     - name: checkout
       uses: actions/checkout@v2
 
+    - name: fix up /etc/hosts
+      # https://github.com/actions/virtual-environments/issues/3353
+      run:  |
+        cat /etc/hosts
+        sudo sed -i "/don't remove this line/d" /etc/hosts || true
+
     - name: update PATH
       run:  |
         echo "$HOME/bin"        >> $GITHUB_PATH