[log] Initialize Logger in C++ test framework

Log functions call global_logger->log_vprintf_() without a null check.
The test main.cpp skips the generated setup() (which calls
Logger::pre_setup()), so set up a static Logger before running tests.

tests/components/main.cpp

@@ -1,5 +1,7 @@
 #include <gtest/gtest.h>
 
+#include "esphome/components/logger/logger.h"
+
 /*
 This special main.cpp replaces the default one.
 It will run all the Google Tests found in all compiled cpp files and then exit with the result
@@ -18,6 +20,12 @@ void original_setup() {
 }
 
 void setup() {
+  // Log functions call global_logger->log_vprintf_() without a null check,
+  // so we must set up a Logger before any test that triggers logging.
+  static esphome::logger::Logger test_logger(0);
+  test_logger.set_log_level(ESPHOME_LOG_LEVEL);
+  test_logger.pre_setup();
+
   ::testing::InitGoogleTest();
   int exit_code = RUN_ALL_TESTS();
   exit(exit_code);