Add simple spec for a github commit attestation

Signed-off-by: Adolfo García Veytia (Puerco) <adolfo.garcia@uservers.net>

Author: puerco

specs/github/commit.yaml

@@ -0,0 +1,12 @@
+# SPDX-FileCopyrightText: Copyright 2025 Carabiner Systems, Inc
+# SPDX-License-Identifier: Apache-2.0
+---
+id: github.com/${ORG}/${REPO}@${REF}
+name: github.com/${ORG}/${REPO}@${REF}
+url: git+https://github.com/${ORG}/${REPO}/@${REF}
+type: http://github.com/carabiner-dev/snappy/specs/commit.yaml
+endpoint: repos/${ORG}/${REPO}/commits/${REF}
+method:  GET
+mask:
+  - sha
+  - url