doc: ctc -> tsc in onboarding extras

PR-URL: nodejs/node#15621
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/onboarding-extras.md

@@ -39,7 +39,7 @@
 | upgrading npm | @fishrock123, @MylesBorins |
 | upgrading V8 | @nodejs/v8, @nodejs/post-mortem |
 
-When things need extra attention, are controversial, or `semver-major`: @nodejs/ctc
+When things need extra attention, are controversial, or `semver-major`: @nodejs/tsc
 
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