tests: fix Content-Length mismatch in test2064

[samueloph]

Spotted when packaging rc2 for Debian, other similar tests (2061-2066) already have crlf="headers" for the Server-side.

[testclutch]

Analysis of PR #22611 at a5eff798:

Test ../../tests/http/test_21_resolve.py::TestResolve::test_21_07_dnsd_a[DoH] failed, which has NOT been flaky recently, so there could be a real issue in this PR. Note that this test has failed in 2 different CI jobs (the link just goes to one of them).

Test ../../tests/http/test_21_resolve.py::TestResolve::test_21_08_dnsd_aaaa[DoH] failed, which has NOT been flaky recently, so there could be a real issue in this PR. Note that this test has failed in 2 different CI jobs (the link just goes to one of them).

Test ../../tests/http/test_21_resolve.py::TestResolve::test_21_09_dnsd_a_delay[DoH] failed, which has NOT been flaky recently, so there could be a real issue in this PR. Note that this test has failed in 2 different CI jobs (the link just goes to one of them).

Test ../../tests/http/test_21_resolve.py::TestResolve::test_21_10_dnsd_aaaa_delay[DoH] failed, which has NOT been flaky recently, so there could be a real issue in this PR. Note that this test has failed in 2 different CI jobs (the link just goes to one of them).

Test ../../tests/http/test_21_resolve.py::TestResolve::test_21_13_dnsd_nxdomain_cached[DoH] failed, which has NOT been flaky recently, so there could be a real issue in this PR. Note that this test has failed in 2 different CI jobs (the link just goes to one of them).

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