gh-38685: Loosen tolerance in a few `expm()` tests
SciPy upstream just merged https://github.com/scipy/scipy/pull/21553
which rewrites the matrix exponential in C. I merged this PR to work
around some other bug, and in the process noticed that a few tolerances
will need to be loosened in our test suite.
URL: https://github.com/sagemath/sage/pull/38685
Reported by: Michael Orlitzky
Reviewer(s): Kwankyu Lee
