nixosTests.curl-impersonate: skip failing test

We use a NixOS VM test to execute the upstream tests of curl-impersonate
because they require networking which cannot be mocked easily in the
sandbox.

Of those upstream tests, test_http2_headers spawns nghttpd2, makes
request against it and then tries to parse the logs it emits.
The last step, the parsing of the logs, it extremely fragile and version
dependent. The version of nghttp2 that we carry in nixpkgs is newer than
the one curl-impersonate expects and happens to emit a different log
format.

So to fix the remaining test suite of curl-impersonate, we simply skip
test_http2_headers.

nixos/tests/curl-impersonate.nix

@@ -19,6 +19,9 @@
       We do that by creating a trusted CA and issuing a cert that includes
       all of the test domains as subject-alternative names and then spoofs the
       hostnames in /etc/hosts.
+    - We started skipping the test_http2_headers test due to log format differences
+      between the nghttpd2 version in nixpkgs and the outdated one curl-impersonate
+      uses upstream for its tests.
 */
 
 import ./make-test-python.nix (
@@ -125,7 +128,7 @@ import ./make-test-python.nix (
 
         # Run tests
         cd tests
-        pytest . --install-dir ../usr --capture-interface eth1
+        pytest . --install-dir ../usr --capture-interface eth1 --exitfirst -k 'not test_http2_headers'
       '';
   in
   {