Fix milestone numbers in planning rotation

Why is this change being made?

We're going straight from %12.10 to %13.0, with no %12.11, making our planning rotation off by 1.

How will this merge request impact page speed?

N/A

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what