fix(ci): bump a2ml-validate-action to 6bff6ec (s-expression form support)

a2ml-validate-action PR #26 (merged 2026-06-01) taught the validator to
recognise both TOML-form `name = "x"` AND s-expression form
`(name "x")` identity/version fields. Before this fix, the validator
regex only matched TOML form, so files using the s-expression dialect
(idiomatic in campaign reports and audit registries) reported
"Missing required identity field" even when the field was structurally
present.

panic-attack was still pinned to the pre-fix SHA
(59145c7d1039fa3059b3ecacdb50ee23d7505898). Bumping to 6bff6ec means
docs/campaigns/2026-05-26.a2ml could have stayed in place; the
move to .machine_readable/campaigns/ in the previous commit is
retained as it's semantically correct (the file's own header
describes it as "machine-readable A2ML form") and provides
defence-in-depth.

Closes the last red required check on PR #94.

Author: hyperpolymath

.github/workflows/dogfood-gate.yml

@@ -38,7 +38,7 @@ jobs:
 
       - name: Validate A2ML manifests
         if: steps.detect.outputs.count > 0
-        uses: hyperpolymath/a2ml-validate-action@59145c7d1039fa3059b3ecacdb50ee23d7505898 # main
+        uses: hyperpolymath/a2ml-validate-action@6bff6ec134fc977e86d25166a5c522ddea5c1e78 # main
         with:
           path: '.'
           strict: 'false'