[SPARK-51169][PYTHON] Add Python 3.14 support in Spark Classic

### What changes were proposed in this pull request?
This PR adds the note for Python 3.14 support in setup.py for Spark Classic.

### Why are the changes needed?
it is needed for 3.14 support

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
CI

### Was this patch authored or co-authored using generative AI tooling?
No

Closes #52556 from zhengruifeng/classic_314.

Authored-by: Ruifeng Zheng <ruifengz@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

Author: zhengruifeng

python/packaging/classic/setup.py

@@ -385,6 +385,7 @@ def run(self):
             "Programming Language :: Python :: 3.11",
             "Programming Language :: Python :: 3.12",
             "Programming Language :: Python :: 3.13",
+            "Programming Language :: Python :: 3.14",
             "Programming Language :: Python :: Implementation :: CPython",
             "Programming Language :: Python :: Implementation :: PyPy",
             "Typing :: Typed",