chore: disable flaky tests (#13253)

Discovered while doing the v4.30.0-rc release.

- `async_select_channel.lean`: @hargoniX @algebraic-dev 
- `sync_mutex.lean`: @hargoniX @datokrat

CMakeLists.txt

@@ -127,7 +127,8 @@ if(USE_MIMALLOC)
     # Unnecessarily deep directory structure, but it saves us from a complicated
     # stage0 update for now. If we ever update the other dependencies like
     # cadical, it might be worth reorganizing the directory structure.
-    SOURCE_DIR "${CMAKE_BINARY_DIR}/mimalloc/src/mimalloc"
+    SOURCE_DIR
+    "${CMAKE_BINARY_DIR}/mimalloc/src/mimalloc"
   )
   FetchContent_MakeAvailable(mimalloc)
 endif()

tests/CMakeLists.txt

@@ -290,7 +290,13 @@ add_test_pile(../doc/examples *.lean)
 add_test_pile(compile *.lean BENCH PART2)
 add_test_pile(compile_bench *.lean BENCH PART2)
 add_test_pile(docparse *.txt)
-add_test_pile(elab *.lean)
+add_test_pile(
+  elab
+  *.lean
+  EXCEPT
+    async_select_channel.lean # Flaky
+    sync_mutex.lean # Flaky
+)
 add_test_pile(elab_bench *.lean BENCH PART2)
 add_test_pile(elab_fail *.lean)
 add_test_pile(misc *.sh)