claudetool: redact initial commit hash in test fixtures
This was causing failures when switching between Go versions,
because the go version ends up in the go.mod, which changes
the git hash.
diff --git a/claudetool/testdata/multi_commit_review.txtar b/claudetool/testdata/multi_commit_review.txtar
index cbf2464..5c741ce 100644
--- a/claudetool/testdata/multi_commit_review.txtar
+++ b/claudetool/testdata/multi_commit_review.txtar
@@ -38,7 +38,7 @@
-- .run_test --
# Errors
-Test regressions detected between initial commit (a4fd3c2166b35e02a2cde466880e45aea6e6212e) and HEAD:
+Test regressions detected between initial commit (INITIAL_COMMIT_HASH) and HEAD:
1: sketch.dev.TestX: New test is failing