Fix allocation counting in clean_v2_descs_as_dir test.

Without this fix, running this test on its own would fail.

Fixes bug 40099. Bugfix on ade50058 in 0.2.8.1-alpha.

Closes #40099 (closed). Necessary for #40098 (closed).

Gitlab CI at https://github.com/torproject/tor/pull/2065

Since this is a trivial fix in the tests, i think we can safely just merge it to 0.3.5.