smoke: Add note in smoke-tests about checkout ref

[ericywl]

Motivation

I kept trying to run smoke-tests with my changes by selecting the branch from the dropdown, only to have the smoke tests run without changes. Ultimately it is PEBKAC, but I thought it would be great to have a note there so others in the future will know.

Changes

• Add note in smoke-tests about ref checkout
• Remove workflow dispatch input in smoke-tests-ess and smoke-tests-es since you can use the branch dropdown instead.

How to test these changes

Run smoke test workflows with this branch.

[mergify]

This pull request does not have a backport label. Could you fix it @ericywl? 🙏
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-8.x is the label to automatically backport to the 8.x branch.
• 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.