fix(htcc_vtimediff): increase `sigma` fit-param min #1127

Job	Run time
build_timelines	38s
download_test_data (physics, dst)	5s
build_coatjava	1m 53s
download_test_data (detectors, mon)	4s
test_swifjob (physics)	1m 12s
test_swifjob (detectors)	51s
run_monitoring (physics)	1m 41s
run_monitoring (detectors)	1m 54s
run_timelines (physics)	45s
run_timelines (detectors, -n 4 --skip-mya)	4m 9s
Deployment	17s
	13m 29s

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