Subtract time with care for overflow #3345

Job	Run time
build-rti / docker-build	1m 14s
build-trace-tools / run (ubuntu-latest)	4s
check-labels / check	3s
build-rti / native-build (ubuntu-latest)	8s
build-trace-tools / run (macos-latest)	9s
build-rti / native-build (macos-latest)	11s
build-trace-tools / run (windows-latest)	15s
fetch-lf / extract-ref	3s
build-rti / native-build (windows-latest)	12s
unit-tests-multi / run (ubuntu-latest)	23s
unit-tests-multi / run (macos-latest)	12s
unit-tests-single / run (ubuntu-latest)	8s
unit-tests-single / run (macos-latest)	13s
lf-default-flexpret	0s
lf-adaptive	0s
lf-default-arduino	0s
lf-default-zephyr	0s
lf-gedf-np	0s
lf-python	0s
lf-default / regular-tests (ubuntu-latest)	4m 20s
	7m 35s

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