Update codeowners for rich-text components (#2069)

# Pull Request

## 🤨 Rationale

vikisekarNI is apparently no longer a valid owner, so replacing with
vivinkrishna-ni.

## 👩‍💻 Implementation

See above.

## 🧪 Testing

N/A

## ✅ Checklist


- [x] I have updated the project documentation to reflect my changes or
determined no changes are needed.

---------

Co-authored-by: Milan Raj <rajsite@users.noreply.github.com>

.github/CODEOWNERS

@@ -16,8 +16,8 @@
 /packages/nimble-components @rajsite @jattasNI
 /packages/nimble-components/.storybook @rajsite @jattasNI @fredvisser
 /packages/nimble-components/src/wafer-map @rajsite @jattasNI @DStavilaNI @zszilagy
-/packages/nimble-components/src/rich-text-viewer @rajsite @jattasNI @vikisekarNI
-/packages/nimble-components/src/rich-text-editor @rajsite @jattasNI @vikisekarNI
+/packages/nimble-components/src/rich-text @rajsite @jattasNI @vivinkrishna-ni
+/packages/nimble-components/src/rich-text-mention @rajsite @jattasNI @vivinkrishna-ni
 /packages/nimble-tokens @rajsite @jattasNI @fredvisser
 /packages/site @rajsite @jattasNI
 /packages/xliff-to-json-converter @rajsite @TrevorKarjanis @jattasNI