kasan: mark kasan_kunit_executing as static

Mark kasan_kunit_executing as static, as it is only used within
mm/kasan/report.c.

Link: https://lkml.kernel.org/r/f64778a4683b16a73bba72576f73bf4a2b45a82f.1672794398.git.andreyknvl@google.com
Fixes: c8c7016f ("kasan: fail non-kasan KUnit tests on KASAN reports")
Reported-by: Nkernel test robot <lkp@intel.com>
Signed-off-by: NAndrey Konovalov <andreyknvl@google.com>
Reviewed-by: NMarco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>

mm/kasan/report.c

@@ -119,7 +119,7 @@ EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
  * Whether the KASAN KUnit test suite is currently being executed.
  * Updated in kasan_test.c.
  */
-bool kasan_kunit_executing;
+static bool kasan_kunit_executing;
 
 void kasan_kunit_test_suite_start(void)
 {