Tutorial: Fix-up typos and inconsistencies

• Fix typo in Step 2
• Fix incorrect code referenced in Step 3, TODO 7. Update comments in MathFunctions/CMakeLists.txt to unique strings.
• Resolve inconsistencies between steps in MathFunctions/CMakeLists.txt

added area:doc workflow:in-review labels

changed milestone to %3.28.0

assigned to @brad.king

Do: stage

added workflow:nightly-testing label and removed workflow:in-review label

Do: merge

mentioned in commit c7c15105

merged

removed workflow:nightly-testing label