gh-108303: Update test_fractions for new Lib/test/mathdata/ (#109686)

Author: vstinner

Lib/test/test_fractions.py

@@ -18,7 +18,7 @@
 
 #locate file with float format test values
 test_dir = os.path.dirname(__file__) or os.curdir
-format_testfile = os.path.join(test_dir, 'formatfloat_testcases.txt')
+format_testfile = os.path.join(test_dir, 'mathdata', 'formatfloat_testcases.txt')
 
 class DummyFloat(object):
     """Dummy float class for testing comparisons with Fractions"""