DOC: fix label links in MAINTAINING.md
DOC: fix label links in MAINTAINING.md

intellij-rust/intellij-rust,Undin/intellij-rust,intellij-rust/intellij-rust,intellij-rust/intellij-rust,intellij-rust/intellij-rust,Undin/intellij-rust,Undin/intellij-rust,intellij-rust/intellij-rust,Undin/intellij-rust,Undin/intellij-rust,intellij-rust/intellij-rust,Undin/intellij-rust