Install script prints misleading message when you already have the version specified by `--version`

Start with the curlable installation script and reproduce both commands using an explicitly requested version and the default latest version. Trace the branch that reports an installed version, then verify that the message distinguishes the requested version from the latest version and preserves the existing latest-version wording.

• Poetry version: 1.5.1
• Python version: 3.9.16
• OS version and name: macOS 13.2.1
• pyproject.toml: n/a

• I am on the latest stable Poetry version, installed using a recommended method.
• I have searched the issues of this repo and believe that this is not a duplicate.
• I have consulted the FAQ and blog for any relevant entries or release notes.
• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option) and have included the output below.

Issue

When installing Poetry from the curl'able script, it conflates "already have requested version" and "already have latest version", which is misleading. An example terminal session:

$ curl -sSL https://install.python-poetry.org | python3.9 - --version 1.5.0

[ snip ]

Installing Poetry (1.5.0): Done

Poetry (1.5.0) is installed now. Great!

You can test that everything is set up by executing:

`poetry --version`


$ curl -sSL https://install.python-poetry.org | python3.9 - --version 1.5.0
Retrieving Poetry metadata

The latest version (1.5.0) is already installed.


$ curl -sSL https://install.python-poetry.org | python3.9 -

[ snip ]

Installing Poetry (1.5.1): Done

Poetry (1.5.1) is installed now. Great!

You can test that everything is set up by executing:

`poetry --version`

1.5.1 is latest, but when I reinstall 1.5.0 explicitly, it calls it the "latest version (1.5.0)".

This was briefly misleading as I was fixing some install issues on my project this morning. The issues themselves were resolved by upgrading Poetry, but I didn't realize at first that this was an option because this version pinning was being done by a set-everything-up script and the logging, of course, implied that upgrading Poetry was not a potential solution.

I would suggest splitting the logging into a two branches for clarity:

• The requested version (x.y.z) is already installed. The latest version is a.b.c.
• The latest version (x.y.z) is already installed.