borgmatic: disable test with TOCTOU race on x86_64-darwin

test_log_outputs_includes_error_output_in_exception has a race between
process.poll() in raise_for_process_errors (returns None) and the
while-loop exit check (returns non-None), so CalledProcessError is
never raised. Timing-dependent; reproduces on x86_64-darwin.

Signed-off-by: Sirio Balmelli <sirio@b-ad.ch>

pkgs/by-name/bo/borgmatic/package.nix

@@ -35,9 +35,14 @@ python3Packages.buildPythonApplication rec {
     ++ optional-dependencies.apprise;
 
   # - test_borgmatic_version_matches_news_version
-  # The file NEWS not available on the pypi source, and this test is useless
+  #   NEWS file not available on the pypi source
+  # - test_log_outputs_includes_error_output_in_exception
+  #   TOCTOU race in log_outputs(): process.poll() returns None in
+  #   raise_for_process_errors but non-None in the while-loop exit check,
+  #   so the error is never raised. Timing-dependent; fails on x86_64-darwin.
   disabledTests = [
     "test_borgmatic_version_matches_news_version"
+    "test_log_outputs_includes_error_output_in_exception"
   ];
 
   nativeBuildInputs = [ installShellFiles ];