gh-38352: Fix a minor typo
Just a minor typo. Previously the math doesn't render on the website
correctly. https://doc.sagemath.org/html/en/reference/arithmetic_curves/
sage/schemes/elliptic_curves/period_lattice.html#sage.schemes.elliptic_c
urves.period_lattice.extended_agm_iteration
Fixed version in documentation preview: https://doc-pr-38352--sagemath.n
etlify.app/html/en/reference/arithmetic_curves/sage/schemes/elliptic_cur
ves/period_lattice.html#sage.schemes.elliptic_curves.period_lattice.exte
nded_agm_iteration
### :memo: Checklist
- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.
URL: https://github.com/sagemath/sage/pull/38352
Reported by: user202729
Reviewer(s): Sebastian A. Spindler
