t7501: rename commit test to comply with naming convention

The naming convention was documented [1] but this script was not
renamed.

The original commit message indicates the script tests basic commit
functionality. Clean up the test name by changing the file name to
specify the intent as documented in the initial commit.

[1] f50c9f7 ("Rename some test scripts and describe the naming convention", 2005-05-15)

Signed-off-by: Stephen P. Smith <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: Stephen P. Smith