Turborepo should own turborepo-tests (vercel#4658)

Updating OWNERS

Author: Greg Soltis

.github/CODEOWNERS

@@ -15,6 +15,7 @@
 .github/workflows/pr-js-tests-*.yml @vercel/turbo-oss
 /version.txt @vercel/turbo-oss
 .github/turborepo-release.yml @vercel/turbo-oss
+/turborepo-tests @vercel/turbo-oss
 
 # Nobody owns these files, so nobody should get tagged on changes
 Cargo.lock