Fix Four Tests for 2021

[oleibman]

Four date tests omit year and therefore default to current year,
which means that the test results must be updated yearly.

This is:

- [x] a bugfix (testing only)
- [ ] a new feature

Checklist:

• Changes are covered by unit tests
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change
• Documentation is updated as necessary

Why this change is needed?

Required annual change to confirm that PhpSpreadsheet uses current year when year is omitted in certain functions.

[oleibman]

Not sure what Scrutinizer problem is. Doesn't really matter - #1774 got here first, so closing this request in favor of that one.