Add --dry-run CLI argument

If the `--dry-run`/`-n` argument is passed, `updatebot` will not push
any changes to the remote repository or open/update a pull request.

updatebot.py

@@ -220,6 +220,7 @@ class Config(pydantic.BaseModel):
 class Arguments:
     config: Path
     branch_name: str
+    dry_run: bool
     projects: list[str]
 
 
@@ -247,6 +248,7 @@ def parse_args() -> Arguments:
         default=XDG_CONFIG_HOME / 'updatebot' / 'config.toml',
     )
     parser.add_argument('--branch-name', '-b', default='updatebot')
+    parser.add_argument('--dry-run', '-n', action='store_true', default=False)
     parser.add_argument('projects', metavar='project', nargs='*', default=[])
     return parser.parse_args(namespace=Arguments())
 
@@ -321,6 +323,7 @@ def main() -> None:
                 repo, f'refs/remotes/origin/{args.branch_name}'
             )
         )
+        if not args.dry_run:
             repo.remote().push(force=True)
             config.repo.create_pr(title, args.branch_name, config.repo.branch)