gh-35163: Fix the documentation for the so matrix Lie algebra
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### 📚 Description
The documentation for the `so` matrix Lie algebra is wrong as the
bilinear form used to construct the Lie group is different (`SO` fixes
any bilinear form, the standard one (dot product) gives the classical
orthogonal matrix definition). We fix this here.
### 📝 Checklist
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URL: https://github.com/sagemath/sage/pull/35163
Reported by: Travis Scrimshaw
Reviewer(s): Frédéric Chapoton
