build(deps): bump github.com/open-policy-agent/opa from 1.8.0 to 1.9.0

Bumps [github.com/open-policy-agent/opa](https://github.com/open-policy-agent/opa) from 1.8.0 to 1.9.0.
- [Release notes](https://github.com/open-policy-agent/opa/releases)
- [Changelog](https://github.com/open-policy-agent/opa/blob/main/CHANGELOG.md)
- [Commits](https://github.com/open-policy-agent/opa/compare/v1.8.0...v1.9.0)

---
updated-dependencies:
- dependency-name: github.com/open-policy-agent/opa
  dependency-version: 1.9.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

vendor/github.com/lestrrat-go/dsig/Changes

@@ -0,0 +1,5 @@
+Changes
+=======
+
+v1.0.0 - 18 Aug 2025
+* Initial release