fix(ci): pin the root-dominance corpus to the shadow-stack lowering

changelog.d/7415-dominance-corpus.md

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+**Fixed** the `GC Root Dominance` gate has been unable to return a verdict since
+#7370 made statepoints the default.
+
+The checker's entire vocabulary is `call void @js_shadow_slot_bind(...)`. Under
+the stack-map lowering the final IR pass resolves those indices to native allocas
+and **removes the calls** (`FunctionCodegen::stack_map_slot_count`), so the corpus
+compiled 144 modules containing **zero** root stores. The gate reported
+`violations: 0` and then correctly refused to pass, because its `--min-binds`
+liveness floor caught that its own subject never ran — CLAUDE.md's fourth hazard,
+working as designed.
+
+Both corpus scripts now pin `PERRY_RS4GC=0`. That is sound rather than a dodge:
+#7340 split the root-set *analysis* from its lowering, and this gate is about the
+analysis, which both backends share. The shadow stack also remains the production
+lowering wherever the runtime cannot walk frames.
+
+Measured, same binary and source, only the knob differing:
+
+```
+arm=default   js_shadow_slot_bind calls = 0     ← reproduces the CI signature
+arm=rs4gc0    js_shadow_slot_bind calls = 9
+```
+
+#7370 already fixed the equivalent breakage in the unit tests — `helpers.rs`
+records that eight tests broke when the default flipped and were given
+`NativeRootsPin::shadow()`. The corpus shell scripts were the same breakage in a
+different idiom, and were missed.