Force braces around multi-line statements (#3094)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

esphome/components/text_sensor/filter.cpp

@@ -64,9 +64,10 @@ optional<std::string> PrependFilter::new_value(std::string value) { return this-
 // Substitute
 optional<std::string> SubstituteFilter::new_value(std::string value) {
   std::size_t pos;
-  for (size_t i = 0; i < this->from_strings_.size(); i++)
+  for (size_t i = 0; i < this->from_strings_.size(); i++) {
     while ((pos = value.find(this->from_strings_[i])) != std::string::npos)
       value.replace(pos, this->from_strings_[i].size(), this->to_strings_[i]);
+  }
   return value;
 }