Add TSAN suppressions for FileLogger2 false positives

TSAN doesn't properly track happens-before relationship between mutex
creation in make_unique and first cross-thread access, even though
std::thread::thread provides the synchronization guarantee. The mutex
is properly protected: base class constructor acquires/releases it
before StatusChangeLogger subscribes to callbacks, and writer thread
acquires it before setting the ready flag.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: facontidavide

tests/tsan_suppressions.txt

@@ -2,3 +2,13 @@
 
 # ZeroMQ false positives
 race:zmq::epoll_t::add_fd
+
+# FileLogger2 false positive: TSAN doesn't properly track happens-before
+# relationship between mutex creation in make_unique and first cross-thread
+# access, even though std::thread::thread provides the synchronization.
+# The mutex is properly protected: base class constructor acquires/releases it
+# before StatusChangeLogger subscribes to callbacks, and writer thread acquires
+# it before setting ready flag.
+mutex:BT::FileLogger2
+race:BT::FileLogger2::callback
+race:BT::FileLogger2::writerLoop