lambda-promtail getUnixSecNsec does not handle nanoseconds with leading zeros

[zephyap]

Describe the bug
The getUnixSecNsec function in tools/lambda-promtail/s3.go does not properly parse timestamp strings where the number of nanoseconds is low i.e. there are leading zeros in the nanosecond part of the string

To Reproduce
Add the following test case to TestGetUnixSecNsec in tools/lambda-promtail/s3_test.go

{
	name: "timestamp_in_nanoseconds_single_digit",
	args: args{
		s: "1234567890000000009",
	},
	expectedSec:  1234567890,
	expectedNsec: 9,
	wantErr:      false,
},

Expected behavior
Above test case should pass, but instead it returns a value of 900000000 for nsec

Environment:
N/A

Screenshots, Promtail config, or terminal output
N/A

[zephyap]

I ran into this when writing a custom parser, so I have a fix that I can contribute! But I wanted to check first if my understanding of the function's intended behaviour is correct