build(deps): bump sigstore-protobuf-specs from 0.4.2 to 0.4.3 (#1435)

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

pyproject.toml

@@ -38,7 +38,7 @@ dependencies = [
   "rfc8785 ~= 0.1.2",
   "rfc3161-client >= 1.0.2,< 1.1.0",
   # NOTE(ww): Both under active development, so strictly pinned.
-  "sigstore-protobuf-specs == 0.4.2",
+  "sigstore-protobuf-specs == 0.4.3",
   "sigstore-rekor-types == 0.0.18",
   "tuf ~= 6.0",
   "platformdirs ~= 4.2",