Change location where test runner gets updated test cases

[mhucka]

The SourceForge location is hardwired into the test runner. We need to change that to use a GitHub location.

[luciansmith]

@fbergmann Was this done?

[fbergmann]

I checked the code and it was not changed in the last 5 years since this issue was opened. I'm not sure how urgent it would be. Here is the file that would need changing https://github.com/sbmlteam/sbml-test-suite/blob/release/src/test-runner/testsuite-core/src/org/sbml/testsuite/core/Util.java