Using Git in the Real World: update git workflow diagram - #31521

Because

The existing diagram does not accurately represent the behavior of git fetch upstream. Fetching from the upstream remote updates the local remote-tracking references but does not update the local main branch. Clarifying this distinction makes the diagram more accurate and helps learners better understand how Git fetch and merge operations work.

This PR

• Updates the git command in the diagram from git fetch upstream/main to git fetch upstream
• Changes the description of the local repository after fetching to indicate that the remote-tracking references have been updated

Issue

Closes #31493

Additional Information

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