Avoid assertion violation when comparing with main-thread

* src/thread.c (unmark_main_thread): New function.
* src/lisp.h (unmark_main_thread): Prototype it.
* src/alloc.c (garbage_collect_1): Call it after sweeping.
(Bug#33073)

* test/src/thread-tests.el (threads-test-bug33073): New test.

1 files changed, 4 insertions, 0 deletions

diff --git a/test/src/thread-tests.el b/test/src/thread-tests.el
index e8d66b87db3..b57b4f9412d 100644
--- a/test/src/thread-tests.el
+++ b/test/src/thread-tests.el
@@ -347,4 +347,8 @@
     (should (= (length (all-threads)) 1))
     (should (equal (thread-last-error) '(error "Die, die, die!")))))
 
+(ert-deftest threads-test-bug33073 ()
+  (let ((th (make-thread 'ignore)))
+    (should-not (equal th main-thread))))
+
 ;;; threads.el ends here