fix: pyproject.toml: remove pin on gunicorn

[vladimir-mencl-eresearch]

The gunicorn package was pinned to 25.0.3 to avoid a deadlock issue introduced in guncorn 25.1.0: benoitc/gunicorn#3529

This has been fixed in benoitc/gunicorn#3520 and the fix was released in guincorn 25.2.0

Remove the explicit pin to last version before the issue (==25.0.3) and instead bump lower bound to the first version fixing the issue.

Run uv sync to update the uv.lock.

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[vladimir-mencl-eresearch]

@theseal , did the tests fail because they try to fetch https://pre.eidas.gov.gr/EidasNode/ConnectorMetadata and that URL was unreachable?

[vladimir-mencl-eresearch]

@theseal ... and after pre.eidas.gov.gr came back online, rerunning tests just worked.

Would you be OK to merge this? When installing 2.1.7, I saw it downgraded my gunicorn, so I checked why - and when I saw the pin, I looked into the underlying reasons and found the fix in gunicorn was released pretty much right away, so if we avoid the broken version, we should not have to pin.

(And sticking to an old version would stop us from getting any security fixes).