Setting --shadow-file makes dmypy reload daemon(perf issue)

This is a bug report.

• Minimal repro

$ touch test.py
$ cp test.py /tmp/test.py
$ dmypy run test.py
Daemon started
Success: no issues found in 22 source files
$ dmypy run test.py
Success: no issues found in 1 source file
$ dmypy run -- --shadow-file test.py /tmp/test.py test.py 
Restarting: configuration changed
Daemon stopped
Daemon started
Success: no issues found in 22 source files

• What is the actual behavior/output?
  dmypy interprets setting --shadow-file as a "configuration change" and reloads the mypy daemon. This effectively counteracts the whole point of having a daemon since it takes a long time to reload the daemon.
• What is the behavior/output you expect?
  dmypy should not interpret --shadow-file changes as configuration changes. It should use the existing daemon instead of reloading.
• What are the versions of mypy and Python you are using?
  Python 3.8.2.
  mypy 0.790+dev.2e9afec83a5214f4a0eaf57a96034230b8460379
  The mypy install is from Github master as of thirty minutes ago.
• What are the mypy flags you are using? (For example --strict-optional)
  The repro above describes this. There are no mypy.ini (or friends) files in the directory.

Beginne damit, nachzuverfolgen, wie dmypy die Option --shadow-file verarbeitet und entscheidet, dass sich die Konfiguration geändert hat. Verwende die minimale Reproduktion, um zu überprüfen, dass das Ändern der Shadow-Datei den Daemon weder stoppt noch neu startet, während die Typprüfung mit der erwarteten Anzahl an Quelldateien weiterhin erfolgreich ist.