rustup; bring back mir-opt-level 3

ci.sh

@@ -25,8 +25,7 @@ function run_tests {
   ./miri test --locked
   if ! [ -n "${MIRI_TEST_TARGET+exists}" ]; then
     # Only for host architecture: tests with MIR optimizations
-    #FIXME: Only testing opt level 1 due to <https://github.com/rust-lang/rust/issues/77564>.
-    MIRIFLAGS="-Z mir-opt-level=1" ./miri test --locked
+    MIRIFLAGS="-Z mir-opt-level=3" ./miri test --locked
   fi
   # "miri test" has built the sysroot for us, now this should pass without
   # any interactive questions.

rust-version

@@ -1 +1 @@
-efbaa413061c2a6e52f06f00a60ee7830fcf3ea5
+c9ced8523bbb90561385aab305232f2167228a83