Poetry: Duplicate entries when running poetry update --dry-run

[MarcoGlauser]

• [x] I am on the latest Poetry version.
• [x] I have searched the issues of this repo and believe that this is not a duplicate.
• [ ] If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: Ubuntu 20.04
• Poetry version: 1.1.1
• Link of a Gist with the contents of your pyproject.toml file: https://gist.github.com/MarcoGlauser/804cbf48001f7a7d1d94d6da9bc88071

Issue

The command poetry update --dry-run duplicates the output of packages as seen below.

I first noticed it in poetry 1.1.0. I could reproduce it on different machines with the attached gist.

[ahlaw]

Hi, can I take this issue? I think I found the problem, when the _dry_run attribute is set, the executor writes after passing the _should_write_operation check here and then again inside _do_execute_operation here. _dry_run should be removed from one of those checks.

[abn]

@ahlaw most definitey! Feel free to create a draft PR for this if you want to discuss a solution.