GH Actions: run against PHP 8.3 (#11601)

* GH Actions: run against PHP 8.3

What with PHP 8.3 being close to the first RC, I'd like to suggest enabling runs against PHP 8.3 for the linting and test runs.

* Linting passes on PHP 8.3, so I propose to not allow new failures to be introduced there.
* The test runs, however, do not pass against PHP 8.3, so I'm marking those as `experimental` for now to allow for fixing the issue(s).

As for the compatibility issues (based on the test runs):
* PR 11599 fixes all known deprecation notices.
* There is, however, one test failure, which I'm not exactly sure how to fix, so I'm leaving this for the maintainers to decide upon.
    Details:
    Prior to PHP 8.3, `ReflectionMethod` could set a `private` method on a parent class to accessible. This is no longer possible in PHP 8.3 since php/php-src 9470 and breaks the `Composer\Test\Repository\ComposerRepositoryTest::testWhatProvides` test.
    Also see: https://3v4l.org/8YcIk/rfc#vgit.master

* GH Actions: update addition of PHP 8.3

* Don't add PHP 8.3 to the `lint` workflow.
* Replace the PHP 8.2 extra builds instead of adding to them for `test`.
* Don't allow builds to fail.

---------

Co-authored-by: jrfnl <jrfnl@users.noreply.github.com>

.github/workflows/continuous-integration.yml

@@ -31,6 +31,7 @@ jobs:
           - "8.0"
           - "8.1"
           - "8.2"
+          - "8.3"
         dependencies: [locked]
         os: [ubuntu-latest]
         experimental: [false]
@@ -55,11 +56,11 @@ jobs:
             os: macos-latest
             dependencies: locked
             experimental: false
-          - php-version: "8.2"
+          - php-version: "8.3"
             dependencies: lowest-ignore
             os: ubuntu-latest
             experimental: false
-          - php-version: "8.2"
+          - php-version: "8.3"
             dependencies: highest-ignore
             os: ubuntu-latest
             experimental: false