fix(docs): sidebar item label impact the pagination label of docs

[Abdullah-03]

…file name as pagination label rather than the sidebar 'label' defined through item definition

Fixes #9781

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

Bug fix

Test Plan

Ran local tests which passed and compiled the demo website to ensure that it runs and the bug is fixed.

Sample Doc file used without H1 or Title:

test

Properties set in sidebar:

{
      type: 'doc',
      label: 'Quick Start test',
      id: 'test',
}

Results (2nd screenshot is of page before test, so see the next button to view updated pagination label):

Test links

Deploy preview: https://deploy-preview-10025--docusaurus-2.netlify.app/

Related issues/PRs

#9781

[netlify]

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 71	🟢 98	🟢 96	🟢 100	🟠 88	Report
/docs/installation	🟠 70	🟢 96	🟢 100	🟢 100	🟠 88	Report
/docs/category/getting-started	🟠 74	🟢 100	🟢 100	🟢 90	🟠 88	Report
/blog	🟠 70	🟢 100	🟢 100	🟢 90	🟠 88	Report
/blog/preparing-your-site-for-docusaurus-v3	🟠 63	🟢 96	🟢 100	🟢 100	🟠 88	Report
/blog/tags/release	🟠 70	🟢 100	🟢 100	🟠 80	🟠 88	Report
/blog/tags	🟠 75	🟢 100	🟢 100	🟢 90	🟠 88	Report

[slorber]

LGTM thanks 👍