gh-138122: Default highlight to sh

[hugovk]

The shell-session is for:

Lexer for Bash shell sessions, i.e. command lines, including a prompt, interspersed with output.

However, these examples don't have $ prompts and output, so better to use sh:

Lexer for (ba|k|z|)sh shell scripts.

https://pygments.org/docs/lexers/#lexers-for-various-shells

Before

https://docs.python.org/3.15/library/profiling.sampling.html#the-attach-command

After

https://cpython-previews--143782.org.readthedocs.build/en/143782/library/profiling.sampling.html#the-attach-command

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📚 Documentation preview 📚: https://cpython-previews--143782.org.readthedocs.build/en/143782/library/profiling.sampling.html

• Issue: Implement PEP 799 – A dedicated profiling package for organizing Python profiling tools #138122