Add token not working issue to upgrade instructions

What does this MR do?

This docs update to upgrade instructions is trying to cover the issue that a customer encountered after upgradeing to 14.0 Gitlab.

After upgrading to GitLab 14.0.12 from 13.5, they noticed that some external pipelines that were using user impersonation tokens to clone internal/public GitLab projects stopped working. After narrowing down the issue to only two users, eliminating any possible client-side issues, we managed to find out that there was a security issue fixed in the 13.12.2 security release: Insufficient Expired Password Validation. This meant that all users with expired passwords should not be allowed to successfully log in using tokens as well.

For more details read the internal support ticket

Related issues

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
• Follow the:
  • Documentation process.
  • Documentation guidelines.
  • Style Guide.
• If you're adding or changing the main heading of the page (H1), ensure that the product tier badge is added.
• If you are a GitLab team member, request a review based on:
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  • The associated Technical Writer.

If you are a GitLab team member and only adding documentation, do not add any of the following labels:

• ~"frontend"
• ~"backend"
• ~"type::bug"
• ~"database"

These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

Documentation-related MRs should be reviewed by a Technical Writer for a non-blocking review, based on Documentation Guidelines and the Style Guide.

If you aren't sure which tech writer to ask, use roulette or ask in the #docs Slack channel.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
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  • Ensure the appropriate labels are added to this MR.
  • Ensure a release milestone is set.
  • If relevant to this MR, ensure content topic type principles are in use, including:
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    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
    • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
• Review by assigned maintainer, who can always request/require the reviews above. Maintainer's review can occur before or after a technical writer review.