fix(heat-map): Show last 8 months of activity

[flower17]

Pre-Submission Checklist

• Your pull request targets the staging branch of freeCodeCamp.
• Branch starts with either fix/, feature/, or translate/ (e.g. fix/signin-issue)
• You have only one commit (if not, squash them into one commit).
• All new and existing tests pass the command npm test. Use git commit --amend to amend any fixes.

Type of Change

• Small bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would change existing functionality)
• Add new translation (feature adding new translations)

Checklist:

• Tested changes locally.
• Addressed currently open issue: Heat map shows only the first 8 months on freeCodeCamp (public portfolio page) #17320

Closes #17320

Description

Fixed issue with HeatMap showing only the first 8 months of user's activity:
#17320

All unit tests passed:
total: 1481
passing: 1481
duration: 17s

Tested the fix locally using test heat map data instead of calendar data coming via props to HeatMap.jsx. Test heat map data contains dates starting from Jul 17 2016 till Jul 17 2018 (2 years range), and tests confirm that there is up to 8 last months of activity is displayed on a heat map.

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[flower17]

Hi @vikaskyadav, please take a look once you have a chance.

This is a new pull request instead of #17893 - created a new one since had issues with amending changes to existing pull request.
Contains same changes as closed pull request(17893), also added storage of the expression result as constant, as you have suggested.

Thank you.