build(deps): bump openpolicyagent/opa in /examples/ext_authz

Bumps openpolicyagent/opa from 0.53.1-istio to 1.9.0-istio.

---
updated-dependencies:
- dependency-name: openpolicyagent/opa
  dependency-version: 1.9.0-istio
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

examples/ext_authz/Dockerfile-opa

@@ -1 +1 @@
-FROM openpolicyagent/opa:0.53.1-istio@sha256:b4821d33fdbca4fe3d2ff85e3f4a18d292f2fb32fe7db995b9239d7242702bab
+FROM openpolicyagent/opa:1.9.0-istio@sha256:a3f146f173dcbb8d99df0fb3ef76a7203863af8b996cff10899b81167dc0a542