Finish the sanitize pass in tests/ #16

Commit 1a25d8a ("sanitize public repository surface") renamed fixture strings in lib/ but touched no test files. #10 fixed the two assertions that were failing as a result, but the sanitization itself is still incomplete: tests/ retains Alex Goodwin in several places, in a public repo.

Not swept in #10 because two of those tests assert on edit distance:

'"Alex" vs "Alex Goodwin" -> 8 (caught by prefix, not distance)'

Renaming to Alex Rivera makes that distance 7, so the assertions and their explanatory comments need recomputing rather than find-and-replace. Small, but it needs attention rather than a sed.