Update instructions for 8.x patch releases

[isaacaflores2]

Motivation/summary

I ran the patch-release workflow yesterday against the main branch by mistake. This resulted in the automation create no PRs.

Updating the docs to specify that the patch release workflow needs to be ran against the base branch i.e 8.18 for the 8.18.7 patch release.

Release note PRs should also target the relevant base branch.

[github-actions]

🤖 GitHub comments

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Just comment with:

• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)

[mergify]

This pull request does not have a backport label. Could you fix it @isaacaflores2? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-7.17 is the label to automatically backport to the 7.17 branch.
• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
• backport-9./d is the label to automatically backport to the 9./d branch. /d is the digit.
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.