[version] Use C++17 nested namespace syntax (#14240)

esphome/components/version/version_text_sensor.cpp

@@ -6,8 +6,7 @@
 #include "esphome/core/helpers.h"
 #include "esphome/core/progmem.h"
 
-namespace esphome {
-namespace version {
+namespace esphome::version {
 
 static const char *const TAG = "version.text_sensor";
 
@@ -36,5 +35,4 @@ void VersionTextSensor::setup() {
 void VersionTextSensor::set_hide_timestamp(bool hide_timestamp) { this->hide_timestamp_ = hide_timestamp; }
 void VersionTextSensor::dump_config() { LOG_TEXT_SENSOR("", "Version Text Sensor", this); }
 
-}  // namespace version
-}  // namespace esphome
+}  // namespace esphome::version