gh-38859: `build/pkgs/matroid_database`: mark as math
From https://github.com/passagemath/passagemath/pull/183:
'Currently it appears in the "Other dependencies" section in
https://doc.sagemath.org/html/en/reference/spkg/; it should go in the
"Math" section.'
URL: https://github.com/sagemath/sage/pull/38859
Reported by: gmou3
Reviewer(s): Kwankyu Lee
