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/base64_default.go

@@ -0,0 +1,14 @@
+//go:build purego || !(amd64 || arm64)
+// +build purego !amd64,!arm64
+
+package base64
+
+import "encoding/base64"
+
+// An Encoding is a radix 64 encoding/decoding scheme, defined by a
+// 64-character alphabet.
+type Encoding = base64.Encoding
+
+func newEncoding(encoder string) *Encoding {
+	return base64.NewEncoding(encoder)
+}