Update CODEOWNERS (#425)

Changes "devrel-admin" to "admin" for @googlemaps-samples/admin.

Author: willum070

.github/CODEOWNERS

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-.github/ @googlemaps-samples/devrel-admin
+.github/ @googlemaps-samples/admin
 .github/auto-approve.yml  @googleapis/github-automation
 dist/samples/*/index.js @willum070 @wangela
 samples/*/src/index.ts @willum070 @wangela