Add pytest depedencies to Pipfile

In #6720 I'm adding a `pytest` based testing framework. This adds the
dependencies for those. They have already been merged into our docker
files in the the-process repo preparation for #6720. But by not having
them on our citus main branch it is impossible to make changes to the
Pipfile, because our CI Dockerfiles and master are out of date.

Since #6720 will need some more discussion and might take a few more
weeks to be merged, this takes out the Pipfile changes. By merging this
PR we can unblock new Pipfile changes.

src/test/regress/Pipfile

@@ -8,6 +8,12 @@ mitmproxy = {editable = true, ref = "main", git = "https://github.com/citusdata/
 construct = "==2.9.45"
 docopt = "==0.6.2"
 cryptography = ">=39.0.1"
+pytest = "*"
+psycopg = "*"
+filelock = "*"
+pytest-asyncio = "*"
+pytest-timeout = "*"
+pytest-xdist = "*"
 
 [dev-packages]
 black = "*"