Fix QNN random crash for UT with multi-thread run (#22160)
### Description
Fix random crash for QNN UTs with multi-thread run like
QnnHTPBackendTests.MultithreadHtpPowerCfgDefaultAndRunOption
Root cause, last minute code change
https://github.com/microsoft/onnxruntime/pull/19521/commits/b4e26bd5f929cee7d303aaf7eccd262f7ae4099a
static std::mutex mutex; -> OrtMutex mutex;
missed static.
