Force signature order in test_sig_filter_1 to fix heisenbug

[ctb]

• Is it mergeable?
• make test Did it pass the tests?
• make coverage Is the new code covered?
• Did it change the command-line interface? Only additions are allowed
  without a major version increment. Changing file formats also requires a
  major version number increment.
• Was a spellchecker run on the source code and documentation after
  changes were made?

[codecov]

Codecov Report

Merging #761 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #761   +/-   ##
=======================================
  Coverage   88.42%   88.42%           
=======================================
  Files          30       30           
  Lines        4786     4786           
  Branches       46       46           
=======================================
  Hits         4232     4232           
  Misses        551      551           
  Partials        3        3

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 134748b...67a9356. Read the comment docs.