remove 9.3 renovate

[olegsu]

• chore: remove 9.3 from renovate baseBranches
• chore: remove 9.3 backport rule from mergify

[mergify]

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

• backport-v./d./d./d is the label to automatically backport to the 8./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.

[mergify]

Tick the box to add this pull request to the merge queue (same as @mergifyio queue).

• Queue this pull request