Small docs/release.rst update, mainly to remove git push --tags.

[rwgk]

Description

Improve release documentation safety and clarity

Problem

The current release documentation has potential safety issues and unclear instructions:

• Uses git push --tags which pushes ALL local tags (potentially including experimental/unwanted tags)
• Unclear assumptions about remote repository naming (origin, upstream)

Changes

• Safety improvement: Replace git push --tags with specific git push upstream vX.Y.Z command
• Add explicit warning: Include "do NOT use git push --tags!" to prevent accidental tag pushes
• Clarify remote naming: Add note that documentation assumes upstream refers to https://github.com/pybind/pybind11.git
• Consistency: Update all commands to use upstream remote consistently

Why this matters

Using git push --tags in release documentation is dangerous because:

• It pushes ALL local tags, not just the intended release tag
• Could accidentally push experimental, personal, or malformed tags
• Makes it harder to control exactly what gets published

Suggested changelog entry:

• Placeholder.

---

📚 Documentation preview 📚: https://pybind11--5748.org.readthedocs.build/

[rwgk]

For completeness, I just ran these commands to clean up:

git push upstream --delete archive/llvm_sanitizer_mods
git push upstream --delete archive/pr2198_list_caster_bytes_uint8
git push upstream --delete archive/pr2409_2020_10_18_two_defines
git push upstream --delete archive/pr2672_sideline_cast_shtc_interleaved
git push upstream --delete archive/pr2672_sideline_cast_shtc_interleaved_openspiel_pattern
git push upstream --delete archive/pr2672_test_unique_ptr_member
git push upstream --delete archive/pr2672_use_smart_holder_as_default_v1
git push upstream --delete archive/pr2687_move_holder_test_premature_delete
git push upstream --delete archive/xxx_value_ptr_xxx_holder
git push upstream --delete archive/yclass_v0
git push upstream --delete find_memory_guarded_delete_complete
git push upstream --delete milestones_reached/pr2672_as_deployed_with_cl_358092606
git push upstream --delete open3d-test

All but one tag (open3d-test) were mine.

That one tag was:

commit 34fe2731a631461c74c0f03247753b138313172e (tag: open3d-test)

[rwgk]

I cancelled the workflow to not waste our limited CI time for this trivial change.