testdata: seed sandbox clean base

Stack Verify · Stack Verify · commit d44b09426b73 · 2026-03-25T22:45:47.000-04:00
diff --git a/_test_data/sandbox/clean/base.txt b/_test_data/sandbox/clean/base.txt
@@ -1,3 +1,3 @@
 clean stack: base branch
 purpose: baseline parent PR
-marker: 549891f
+marker: 2983e05
