test: standardize to 8 character commit SHA1 in assert_contributor_names

[cpb]

This PR adds a script which provides a CLI similar to rails test, but runs the suite with a version of assert_contributor_names which:

1. Resolves test failures from ambiguous OID exceptions by finding the unambiguous SHA1 prefix which passes the original assertion, and rewrites the assert_contributor_names call with the unambiguous SHA1 prefix.
2. Rewrites the assert_contributor_names calls which pass with an 8 character long SHA1.

Example output running bin/lengthen-sha1 compared to bin/rails test. Note the difference in number of assertions: bin/lengthen-sha1 won't rewrite a SHA1 in an assert_contributor_names which does not pass with the original expectation.

$ bin/lengthen-sha1
Run options: --seed 18175

# Running:

...........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
Ambiguous sha1 842ce34 was lengthened to 842ce34b to pass rails test test/credits/canonical_names_test.rb:1463
...........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
Ambiguous sha1 a5991d8 was lengthened to a5991d84 to pass rails test test/credits/canonical_names_test.rb:2067
..........................................................................................................................

Finished in 35.047266s, 40.6308 runs/s, 93.2740 assertions/s.
1424 runs, 3269 assertions, 0 failures, 0 errors, 0 skips

$ rails test
Run options: --seed 53663

# Running:

................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

Finished in 18.365159s, 77.5381 runs/s, 100.2986 assertions/s.
1424 runs, 1842 assertions, 0 failures, 0 errors, 0 skips

This PR includes the modifications form the above example test run in:

• update calls to assert_contributor_names to have 8 character SHA1