build(deps): bump github.com/open-policy-agent/opa from 1.6.0 to 1.8.0

Bumps [github.com/open-policy-agent/opa](https://github.com/open-policy-agent/opa) from 1.6.0 to 1.8.0.
- [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/v1.6.0...v1.8.0)

---
updated-dependencies:
- dependency-name: github.com/open-policy-agent/opa
  dependency-version: 1.8.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

vendor/github.com/segmentio/asm/base64/encode_arm64.go

@@ -0,0 +1,6 @@
+//go:build !purego
+// +build !purego
+
+package base64
+
+func encodeARM64(dst []byte, src []byte, lut *int8) (int, int)