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/skipped_to_failing.txtar b/claudetool/testdata/skipped_to_failing.txtar
index 98935e8..55c12a8 100644
--- a/claudetool/testdata/skipped_to_failing.txtar
+++ b/claudetool/testdata/skipped_to_failing.txtar
@@ -27,7 +27,7 @@
-- .run_test --
# Errors
-Test regressions detected between initial commit (3635353dfefb2fa652728318567209ccfc4aba42) and HEAD:
+Test regressions detected between initial commit (INITIAL_COMMIT_HASH) and HEAD:
1: sketch.dev.TestP: Was skipped, now failing