Docs: avoid unresolved torch.jit Sphinx refs to fix the CICD doc build failure.

[littlebullGit]

What does this PR do?

Fixes #21620

This PR fixes the docs build failure caused by unresolved Sphinx cross-references in LightningModule.to_torchscript().

The immediate source of the warnings is Lightning's docstring in src/lightning/pytorch/core/module.py, which references deprecated torch.jit objects with Sphinx roles:

• torch.jit.ScriptModule
• torch.jit.script
• torch.jit.trace
• torch.jit

These references appear to have become unresolved after upstream PyTorch documentation / intersphinx changes following TorchScript deprecation.

This change keeps the fix targeted by replacing only those broken external torch.jit Sphinx roles with code literals. Other working cross-references remain unchanged.

No breaking changes.

Before submitting

• Did you read the contributor guideline, Pull Request section?
• Did you make sure your PR does only one thing, instead of bundling different changes together?
• Did you verify new and existing tests pass locally with your changes?

Local verification:

• ./.venv/bin/python -m py_compile src/lightning/pytorch/core/module.py

---

📚 Documentation preview 📚: https://pytorch-lightning--21621.org.readthedocs.build/en/21621/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79%. Comparing base (6805188) to head (e9a69b7).
⚠️ Report is 9 commits behind head on master.
✅ All tests successful. No failed tests found.

❗ There is a different number of reports uploaded between BASE (6805188) and HEAD (e9a69b7). Click for more details.

HEAD has 3547 uploads less than BASE

Flag	BASE (6805188)	HEAD (e9a69b7)
cpu	835	42
python	60	3
lightning_fabric	268	0
pytest	418	0
python3.12	239	12
python3.13	176	9
python3.12.7	180	9
lightning	300	15
python3.10	60	3
python3.11	120	6
pytorch2.1	60	6
pytest-full	417	42
pytorch2.4.1	30	3
pytorch_lightning	267	27
pytorch2.10	59	6
pytorch2.2.2	30	3
pytorch2.8	60	6
pytorch2.3	30	3
pytorch2.6	30	3
pytorch2.7	29	3
pytorch2.9	59	6
pytorch2.5.1	30	3

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #21621     +/-   ##
=========================================
- Coverage      87%      79%     -8%     
=========================================
  Files         270      267      -3     
  Lines       23895    23836     -59     
=========================================
- Hits        20675    18762   -1913     
- Misses       3220     5074   +1854     

[deependujha]

great work, but my approach was to ignore them: https://github.com/Lightning-AI/pytorch-lightning/pull/21523/changes#diff-9a7ea5a9d5aab95e64e812eef353aba08036e2416be44508d84bd6298bdab6a9

[bhimrazy]

I think this pr is probably better anyway, since it was coming from deprecated code. I actually remembered the ignore approach from your PR as well.

[deependujha]

in that case, either this method should be discouraged, or removed completely.