[python] Fix invalid pip syntax for httpx/tornado in requirements.txt

[hhuuggoo]

Description of the PR

The httpx and tornado entries in the python generator's
requirements.mustache template were written using TOML / Pipfile-style
name = "spec" assignment syntax, which is not valid in a pip
requirements.txt file. The other entries in the same template
(urllib3, python_dateutil, pydantic, aiohttp, etc.) all use the
correct pip syntax — only these two lines are wrong.

As a result, every Python client generated with --library httpx
fails immediately at pip install -r requirements.txt:

ERROR: Invalid requirement: 'httpx = ">= 0.28.1"': Expected semicolon (after name with no version specifier) or end
    httpx = ">= 0.28.1"
          ^ (from line 2 of requirements.txt)

The same bug would affect --library tornado (same broken pattern on the
line below it in the template), though that path is less commonly used.

What this PR changes

In modules/openapi-generator/src/main/resources/python/requirements.mustache:

 {{#httpx}}
-httpx = ">= 0.28.1"
+httpx >= 0.28.1
 {{/httpx}}
 {{#tornado}}
-tornado = ">= 4.2, < 5"
+tornado >= 4.2, < 5
 {{/tornado}}

And the committed sample at
samples/openapi3/client/petstore/python-httpx/requirements.txt is
regenerated to match.

Scope check — was this bug anywhere else?

I checked the other two python dependency templates:

• python/setup.mustache — not affected. The install_requires
  entries already use correct pip syntax: "httpx >= 0.28.1",
  "tornado>=4.2, < 5".
• python/pyproject.mustache — not affected. Both dependency
  sections are syntactically valid:
  • [tool.poetry.dependencies] uses httpx = ">= 0.28.1", which is
    the correct TOML form for Poetry.
  • [project].dependencies uses "httpx (>=0.28.1)", which is the
    correct PEP 621 form.

So the fix is isolated to requirements.mustache plus its
corresponding sample.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work.
• Run the shell script(s) under ./bin/ (or Windows batch scripts under .\bin\windows) to update Petstore samples related to your fix. (Only the python-httpx sample changed; updated in this PR.)
• File the PR against the correct branch: master branch for non-breaking changes.
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.

cc @OpenAPITools/generator-core-team
cc python technical committee

---

Summary by cubic

Fix pip requirement syntax for httpx and tornado in the Python generator so generated clients install cleanly. Replaces TOML-style name = "spec" with valid pip specifiers and updates the python-httpx sample.

• Bug Fixes
  • In python/requirements.mustache, use httpx >= 0.28.1 and tornado >= 4.2, < 5.
  • Regenerated samples/openapi3/client/petstore/python-httpx/requirements.txt.
  • Verified setup.mustache and pyproject.mustache are already correct (no changes).

^{Written for commit f81d086. Summary will update on new commits.}

Review in cubic

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}

[wing328]

thanks for the fix

i'm able to repeat the issue with #23892

will add that after merging your fix.

[wing328]

FYI. Merged #23892 to update the CI workflow covering the issue moving forward.