Fix: weird expression for contribution analytics

What does this MR do and why?

From the screenshot 👇 it looks quite weird for me to read the texts because it says %d persons contributors. we don't really need the word person here.

This MR removes the unnecessary word person in the text.

/cc @prajnamas @orozot @qk44077907

Screenshots or screen recordings

The following screenshots are the fixed version:

Singular form

Plural form

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

1. Boot GDK with a premium or above license
2. Go to any project > Analytics > Contribution
3. Click on the tabs that has data and observe.

Numbered steps to set up and validate the change are strongly suggested.

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