tests : add pthread to test-wer for freebds

This commit adds pthread to the test-wer target for FreeBSD. This is
necessary to avoid the following error:
```console
[68%] Linking CXX executable ../bin/test-wer
ld: error: undefined reference due to --no-allow-shlib-undefined: pthread_create
>>> referenced by ../src/libwhisper.so.1.7.4
c++: error: linker command failed with exit code 1 (use -v to see invocation)
gmake[2]: *** [tests/CMakeFiles/test-wer.dir/build.make:106: bin/test-wer] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:1421: tests/CMakeFiles/test-wer.dir/all] Error 2
```

Refs: https://github.com/ggerganov/whisper.cpp/actions/runs/14218829646/job/39841747819

Author: danbev

tests/CMakeLists.txt

@@ -85,9 +85,11 @@ if (WHISPER_FFMPEG)
     set_tests_properties(${TEST_TARGET} PROPERTIES LABELS "tiny;mp3")
 endif()
 
+find_package(Threads REQUIRED)
+
 # WER Unit Test
 add_executable(test-wer test-wer.cpp)
 target_include_directories(test-wer PRIVATE ../examples)
-target_link_libraries(test-wer PRIVATE common)
+target_link_libraries(test-wer PRIVATE common ${CMAKE_THREAD_LIBS_INIT})
 add_test(NAME test-wer COMMAND test-wer)
 set_tests_properties(test-wer PROPERTIES LABELS "unit")