Fix overwriting of date in RIS import

[Siedlerchr]

Now the first valid year is taken into account. Previously the year was overwritten when another field containing year was found.
Adjusted the tests to reflect the new behavior. This required adjusting the month field in the test files

Fixes #4816

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• Change in CHANGELOG.md described
• Tests created for changes
• Manually tested changed features in running JabRef
• Screenshots added in PR description (for bigger UI changes)
• Ensured that the git commit message is a good one
• Check documentation status (Issue created for outdated help page at help.jabref.org?)

[tobiasdiez]

LGTM

[CodeSJS]

Thanks for working on this.

The import is now correct for the example I supplied, but it may not be a solid fix. If for some reason the Y2 field precedes Y1 or PY, then I confirmed that the JabRef development master still gets the publication year wrong.

Y2 is access year, should never be imported as publication year, so I guess JabRef should ignore this field. PY, publication year, should be the desired field. Y1 is "primary date". I searched, but could not find out how primary date differs from publication year, other than is a full year-month-day.

Regards,
Sherwin