DOC: Remove TODO from `test_openpyxl`
xref #29862 

Brought up by @jbrockmendel seems the `xfail` has been removed and version has been unpinned, just a tiny PR to remove this `TODO` from tests. probably people who fixed it forgot to remove this.

cc @jbrockmendel 

LGTM, the CI failure is unrelated Thanks @charlesdong1991 