Fix minor typos in airflow-core docs

[vanshtuli-lang]

Fixes a handful of small grammar/typo issues found while reviewing airflow-core docs:

• airflow-core/docs/core-concepts/dags.rst:325 — "decorator come in" → "decorator comes in" (subject-verb agreement)
• airflow-core/docs/core-concepts/dags.rst:842 — "There is a Airflow configuration" → "There is an Airflow configuration" (a/an)
• airflow-core/docs/howto/timetable.rst:350 — "rather then the start" → "rather than the start" (then/than)
• airflow-core/docs/howto/docker-compose/index.rst:250 — "download a optional wrapper scripts" → "download an optional wrapper script" (article/number agreement)

No functional changes, docs only.

[boring-cyborg]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contributors' Guide
Here are some useful points:

• Pay attention to the quality of your code (ruff, mypy and type annotations). Our prek-hooks will help you with that.
• In case of a new feature add useful documentation (in docstrings or in docs/ directory). Adding a new operator? Check this short guide Consider adding an example Dag that shows how users should use it.
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  In case of doubts contact the developers at:
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[uros-b]

LGTM, thank you @vanshtuli-lang!