Edit tests to adjust with changes in libxml2 upgrade

Bug: http://b/307806447
Test: TreeHugger
Change-Id: I5978fb6b11538ac254b971fada17cfbbcc5360cf
diff --git a/audio/common/all-versions/test/utility/tests/utility_tests.cpp b/audio/common/all-versions/test/utility/tests/utility_tests.cpp
index c523066..c2bcfbc 100644
--- a/audio/common/all-versions/test/utility/tests/utility_tests.cpp
+++ b/audio/common/all-versions/test/utility/tests/utility_tests.cpp
@@ -70,6 +70,7 @@
 std::string substitute(const char* fmt, const char* param) {
     std::string buffer(static_cast<size_t>(strlen(fmt) + strlen(param)), '\0');
     snprintf(buffer.data(), buffer.size(), fmt, param);
+    buffer.resize(strlen(buffer.c_str()));
     return buffer;
 }