Fix key for claims

[vsnaichuk]

What this PR is changing or adding?

Corrects the JWT expiration key in claims from expires to exp, aligning it with standard JWT claim specifications. See the GetExpirationTime function in jwt/map_claims.go

Before/after or any other screenshots

Which issues are fixed by this PR?

1. 247

Pre-launch Checklist

• [x] I have read and fully accepted project's code of conduct.
• [x] I listed at least one issue that this PR fixes in the description above.
• [x] I updated/added relevant documentation and/or comments to the code.
• [x] All existing and new tests are passing successfully.

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