aws_util: fix leading zeros in time_key #8249

Job	Run time
run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, gcc)	19m 48s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, clang)	1h 0m 13s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, gcc)	18m 55s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, clang)	17m 27s
run-ubuntu-unit-tests (-DFLB_SMALL=On, gcc)	19m 21s
run-ubuntu-unit-tests (-DFLB_SMALL=On, clang)	18m 52s
run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, gcc)	18m 37s
run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, clang)	18m 36s
run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, gcc)	20m 0s
run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, clang)	18m 49s
run-ubuntu-unit-tests (-DFLB_COVERAGE=On, gcc)	53m 0s
run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, gcc)	18m 53s
run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, clang)	17m 39s
run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, gcc)	18m 36s
run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, clang)	1h 0m 15s
run-macos-unit-tests	0s
Unit tests (matrix)	3s
	6h 39m 4s

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