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/mark_test_skipped.txtar b/claudetool/testdata/mark_test_skipped.txtar
index d834ae4..17f5168 100644
--- a/claudetool/testdata/mark_test_skipped.txtar
+++ b/claudetool/testdata/mark_test_skipped.txtar
@@ -26,7 +26,7 @@
-- .run_test --
# Errors
-Test regressions detected between initial commit (851ba0628e0e2d93e27e168d6af336f3e4d375c7) and HEAD:
+Test regressions detected between initial commit (INITIAL_COMMIT_HASH) and HEAD:
1: sketch.dev.TestP: Was passing, now skipped