[Cleanup] Cleanup uses of insert/push_back when a temp object is used. (#3170)

common/strings.h

@@ -219,7 +219,7 @@ std::vector<std::string> join_pair(
 	std::vector<std::string> output;
 
 	for (const std::pair<T1, T2> &src_iter: src) {
-		output.push_back(
+		output.emplace_back(
 
 			fmt::format(
 				"{}{}{}{}{}{}{}",
@@ -253,7 +253,7 @@ std::vector<std::string> join_tuple(
 
 	for (const std::tuple<T1, T2, T3, T4> &src_iter: src) {
 
-		output.push_back(
+		output.emplace_back(
 
 			fmt::format(
 				"{}{}{}{}{}{}{}{}{}{}{}{}{}{}{}",