Mark packaging tests as non-flaky (#4429)

I’ve spend several hours trying to get them to fail on Linux and
Windows and have failed completely (apart from making my machine roun
out of memory, thanks crashplan). I also inserted explicit delays to
make the failure more often frequent without any sucess (at making it
fail). I don’t really have a satisfying explanation of why this is
gone now. My best guess is that the `ghcide` upgrade fixed this since
it included some fixes and changes around how we kill and start the
shake process.

fixes #4328

changelog_begin
changelog_end

compiler/damlc/tests/BUILD.bazel

@@ -213,8 +213,6 @@ da_haskell_test(
         "//daml-lf/repl",
         "@davl//:released/davl-v3.dar",
     ],
-    # See https://github.com/digital-asset/daml/issues/4328
-    flaky = True,
     hackage_deps = [
         "base",
         "bytestring",