iotests/linters: check mypy files all at once

We can circumvent the '__main__' redefinition problem by passing
--scripts-are-modules. Take mypy out of the loop per-filename and check
everything in one go: it's quite a bit faster.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20210923180715.4168522-4-jsnow@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/297

@@ -74,12 +74,7 @@ def run_linters():
     print('=== mypy ===')
     sys.stdout.flush()
 
-    # We have to call mypy separately for each file.  Otherwise, it
-    # will interpret all given files as belonging together (i.e., they
-    # may not both define the same classes, etc.; most notably, they
-    # must not both define the __main__ module).
     env['MYPYPATH'] = env['PYTHONPATH']
-    for filename in files:
     p = subprocess.run(('mypy',
                         '--warn-unused-configs',
                         '--disallow-subclassing-any',
@@ -91,7 +86,8 @@ def run_linters():
                         '--warn-unused-ignores',
                         '--no-implicit-reexport',
                         '--namespace-packages',
-                            filename),
+                        '--scripts-are-modules',
+                        *files),
                        env=env,
                        check=False,
                        stdout=subprocess.PIPE,