ci(freebsd): enable oldtests

.builds/freebsd.yml

@@ -35,10 +35,6 @@ tasks:
 - unittest: |
     cd neovim
     gmake unittest
-
-# Unfortunately, oldtest is tanking hard on sourcehut's FreeBSD instance
-# and not producing any logs as a result. So don't do this task for now.
-# Ref: https://github.com/neovim/neovim/pull/11477#discussion_r352095005.
-# - test-oldtest: |
-#     cd neovim
-#     gmake oldtest
+- oldtest: |
+    cd neovim
+    gmake oldtest