Remove @nagisa from review rotation

I have been reviewing PRs for a long while during weekends, however
recently I’ve been having trouble commiting to that as well. Every
weekend I’ve been spending working on a house.

I may return myself to the rotation in a couple of months. I may also
just start ninja'ing up some PRs from the PR list whenever I find some
time for reviews again, without putting myself back into the rotation,
in acknowledgement that me being able to review every weekend or every
second weekend is not a great experience for the contributors waiting on
reviews from me.

triagebot.toml

@@ -482,7 +482,6 @@ compiler-team = [
     "@davidtwco",
     "@oli-obk",
     "@lcnr",
-    "@nagisa",
     "@wesleywiser",
     "@michaelwoerister",
 ]
@@ -552,7 +551,6 @@ mir = [
     "@oli-obk",
 ]
 mir-opt = [
-    "@nagisa",
     "@oli-obk",
     "@wesleywiser",
 ]