Fix calculation of expiration timestamp

[mprausa]

currentTimestamp is in millis already which is why it should not be mulitplied by 1000.

The constructor of OicCredentials is called with CLOCK.millis() (here and here) for the currentTimestamp parameter which shows that currentTimestamp is indeed in millis and not seconds.

This bug was introduced in bba32e09 (PR #357).

Testing done

Submitter checklist

• [x] Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• [x] Ensure that the pull request title represents the desired changelog entry
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• [x] Ensure you have provided tests - that demonstrates feature works or fixes the issue

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 71.44%. Comparing base (b7205f1) to head (8e99549). Report is 6 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #359 +/- ## ============================================ - Coverage 72.02% 71.44% -0.58% + Complexity 234 232 -2 ============================================ Files 11 11 Lines 990 991 +1 Branches 142 142 ============================================ - Hits 713 708 -5 - Misses 199 205 +6 Partials 78 78 ```

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[mprausa]

I've added a second commit. I think the other change on the same line done in PR #357 is incorrect as well. We have to subtract allowedClockSkewFixed, so that the token is refreshed earlier not later.

[mprausa]

@michael-doubez Yes, I agree. I've removed the second commit.