Feature/sync gigasecond

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[ahans]

@exercism/cpp here is the new PR. I had forced-pushed to the previous to include the no important files changed tag. I wasn't aware that this would prevent re-opening. Sorry about that!

[SleeplessByte]

The failed check says:

This PR touches files which potentially affect the outcome of 
the tests of an exercise. This will cause all students' solutions
to affected exercises to be re-tested.

If this PR does **not** affect the result of the test (or, for
example, adds an edge case that is not worth rerunning all tests
for), **please add the following to the merge-commit message**
which will stops student's tests from re-running. Please
copy-paste to avoid typos.

[no important files changed]

For more information, refer to the [documentation](https://exercism.org/docs/building/tracks#h-avoiding-triggering-unnecessary-test-runs). 
If you are unsure whether to add the message or not, please ping
`@exercism/maintainers-admin` in a comment. Thank you!

In this case ya probably want to re-run all the student solutions.

[ahans]

In this case ya probably want to re-run all the student solutions.

I only added that one excluded test to tests.toml and renamed the tests. I didn't change any actual test code. The changes there are only formatting (looks like .clang-format has changed in the meantime or hadn't been applied to that file before). So I'm not sure we should really re-run all student solutions. However, I can of course drop the tag. Let me know what to do!

[SleeplessByte]

I didn't see the include false on the last line. If no tests were added (or changed) then indeed, it should NOT re-run ;)

[fcec307c-7529-49ab-b0fe-20309197618a]
description = "does not mutate the input"
include = false