Merge branch 'bugfix/serial_reader_linux_writes_correctly' into 'master'

bugfix(tools): idf.py monitor now reads correctly on Linux

Closes IDF-6317

See merge request espressif/esp-idf!21241

tools/idf_monitor.py

@@ -276,6 +276,7 @@ class LinuxMonitor(Monitor):
 
     def serial_write(self, *args: str, **kwargs: str) -> None:
         self.serial.stdin.write(*args, **kwargs)
+        self.serial.stdin.flush()
 
     def check_gdb_stub_and_run(self, line: bytes) -> None:
         return  # fake function for linux target