test_integral_equation() in test_scalar_int_eq.py: Print statements should be changed to log statements

When redirecting output to a file, the output of print is buffered but the output of the logger isn't. As a result, the print statements (which report some useful metadata*) don't immediately show, which negates their usefulness with long-running examples.

*Data reported by print includes geometry sizes and relative errors for the solve. GMRES residuals are not buffered, so while those are also written to stdout, they work as expected.