Fix CQS signal facebook-hte-BadImplicitCast in xplat/jsi/jsi/test (#57942)

Summary: Pull Request resolved: #57942

Reviewed By: Daniel9z

Differential Revision: D115846369

fbshipit-source-id: f28285263cd970cfb88c9d3aa5c4428e97bd3206

Author: generatedunixname910664361436750

packages/react-native/ReactCommon/jsi/jsi/test/testlib.cpp

@@ -1105,7 +1105,8 @@ namespace {
 
 unsigned countOccurences(const std::string& of, const std::string& in) {
   unsigned occurences = 0;
-  std::string::size_type lastOccurence = -1;
+  std::string::size_type lastOccurence =
+      static_cast<std::string::size_type>(-1);
   while ((lastOccurence = in.find(of, lastOccurence + 1)) !=
          std::string::npos) {
     occurences++;