rotation.single-logger reports archive-log.running baseline difference

[awelzel]

The rotation.single-logger test running at just the right time reports an .archive-log process running, causing a baseline difference and a spurious error.

Failed here: https://cirrus-ci.com/task/5845006406123520?logs=test#L93

[#30] rotation.single-logger ... failed
  % 'btest-diff logger_working_dir.out' failed unexpectedly (exit code 1)
  % cat .diag
  == File ===============================
  .archive-log.running.107908.tmp
  .cmdline
  .env_vars
  .pid
  .startup
  .status
  == Diff ===============================
  --- /dev/fd/63	2023-05-23 14:23:26.691588994 +0000
  +++ /dev/fd/62	2023-05-23 14:23:26.691588994 +0000
  @@ -1,3 +1,4 @@
  +.archive-log.running.107908.tmp
   .cmdline
   .env_vars
   .pid
  =======================================