Update releasenotes.txt (#4404)

Author: chrchr-github

releasenotes.txt

@@ -3,4 +3,5 @@ release notes for cppcheck-2.9
 - restored check for negative allocation (new[]) and negative VLA sizes from cppcheck 1.87 (LCppC backport)
 - replaced hardcoded check for pipe() buffer size by library configuration option (LCppC backport)
 - on Windows the callstack is now being written to the output specific via "--exception-handling"
-- make it possible to disable the various exception handling parts via the CMake options "NO_UNIX_SIGNAL_HANDLING", "NO_UNIX_BACKTRACE_SUPPORT" and "NO_WINDOWS_SEH"
+- make it possible to disable the various exception handling parts via the CMake options "NO_UNIX_SIGNAL_HANDLING", "NO_UNIX_BACKTRACE_SUPPORT" and "NO_WINDOWS_SEH"
+- detect more redundant calls of std::string::c_str(), std::string::substr(), and unnecessary copies of containers