lal_tconvert tests fail on macOS

The tests of lal_tconvert are failing on macOS:

$ make check -C bin/
...
PASS: lal_simd_detect
PASS: lal_version
PASS: test_cache
FAIL: test_tconvert
PASS: test_path2cache
=====================================
   LAL 7.2.0.1: bin/test-suite.log
=====================================

# TOTAL: 5
# PASS:  4
# SKIP:  0
# XFAIL: 0
# FAIL:  1
# XPASS: 0
# ERROR: 0

.. contents:: :depth: 2

FAIL: test_tconvert
===================

+ ./lal_tconvert --rfc-2822 800000000
+ test 'Fri, 13 May 2005 06:13:07 -0800' == 'Fri, 13 May 2005 06:13:07 +0000'
FAIL test_tconvert (exit status: 1)

============================================================================
Testsuite summary for LAL 7.2.0.1
============================================================================
# TOTAL: 5
# PASS:  4
# SKIP:  0
# XFAIL: 0
# FAIL:  1
# XPASS: 0
# ERROR: 0
============================================================================
See bin/test-suite.log
Please report to lal-discuss@ligo.org
============================================================================

I presume this is an issue with locale or similar being different on macOS relative to Linux.

cc @karl-wette (author of lal/bin/test_tconvert)