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/add_skipped_test.txtar b/claudetool/testdata/add_skipped_test.txtar
index 099ebdd..dba6df2 100644
--- a/claudetool/testdata/add_skipped_test.txtar
+++ b/claudetool/testdata/add_skipped_test.txtar
@@ -21,7 +21,7 @@
-- .run_test --
# Errors
-Test regressions detected between initial commit (2cdfdc5009e364add9a263909472f85eb08480ed) and HEAD:
+Test regressions detected between initial commit (INITIAL_COMMIT_HASH) and HEAD:
1: sketch.dev.TestP: New test is skipped