Install jq in the verification script. (#3017)

Turns out cloud build runs the scripts independently and installing on task does not make it available for the next one.

Bug: flutter/flutter#133376

cloud_build/verify_provenance.sh

@@ -12,6 +12,11 @@ PROVENANCE_PATH=$1
 BUILDER_ID=https://cloudbuild.googleapis.com/[email protected]
 SOURCE_URI=github.com/flutter/cocoon
 
+# Download the jq binary in order to obtain the artifact registry url from the
+# docker image provenance.
+echo "Installing jq using apt..."
+apt update && apt install jq -y
+
 # Download slsa-verifier in order to validate the docker image provenance.
 # This takes the version of slsa-verifier defined in tooling/go.mod.
 echo "Installing slsa-verifier using go..."