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/codereview_test.go b/claudetool/codereview_test.go
index 71934a2..0d0c143 100644
--- a/claudetool/codereview_test.go
+++ b/claudetool/codereview_test.go
@@ -140,6 +140,10 @@
 			}
 			want := string(file.Data)
 
+			commitCleaner := strings.NewReplacer(initialCommit, "INITIAL_COMMIT_HASH")
+			got = commitCleaner.Replace(got)
+			want = commitCleaner.Replace(want)
+
 			if update {
 				archive.Files[i].Data = []byte(got)
 				break