Fix error = -> ==

Author: egarbuz

pg_probackup2/app.py

@@ -159,7 +159,7 @@ def _add_options(self, command: list, skip_log_directory: bool):
             command += ['--log-directory=' + self.pb_log_path]
             strcommand += ' ' + command[-1]
 
-        if init_params.major_version = 2:
+        if init_params.major_version == 2:
             if 'pglz' in strcommand and \
                     ' -j' not in strcommand and \
                     '--thread' not in strcommand: