Fix tsan warning about ExecutionCoverage::SetTracing()

See: https://github.com/google/fuzztest/issues/1965
PiperOrigin-RevId: 862829024

fuzztest/internal/coverage.h

diff --git a/fuzztest/internal/coverage.h b/fuzztest/internal/coverage.h
index 8948d52..e908da8 100644
--- a/fuzztest/internal/coverage.h
+++ b/fuzztest/internal/coverage.h
@@ -28,6 +28,7 @@
 #define FUZZTEST_FUZZTEST_INTERNAL_COVERAGE_H_
 
 #include <algorithm>
+#include <atomic>
 #include <cstddef>
 #include <cstdint>
 #include <cstring>
@@ -135,11 +136,13 @@
 
   // Flag marking if the control flow is currently in target codes.
   // We don't want to collect unrelated updates to cmp score and dictionary.
-  bool IsTracing() { return is_tracing_; }
+  bool IsTracing() { return is_tracing_.load(std::memory_order_relaxed); }
 
   // Right before target run, call this method with true; right after
   // target run, call this method with false.
-  void SetIsTracing(bool is_tracing) { is_tracing_ = is_tracing; }
+  void SetIsTracing(bool is_tracing) {
+    is_tracing_.store(is_tracing, std::memory_order_relaxed);
+  }
 
   // Update the PC->max stack usage map for `PC`.
   // It compares the current stack frame against the stack frame specified in
@@ -190,7 +193,7 @@
   std::atomic<bool> new_coverage_{false};
 
   TablesOfRecentCompares tables_of_recent_compares_ = {};
-  bool is_tracing_ = false;
+  std::atomic<bool> is_tracing_{false};
 };
 
 // Set the singleton ExecutionCoverage object.