Use oats from fix PR

Consume changes from grafana/oats#109 to fix matrix usage.

Author: martincostello

.github/workflows/oats.yml

@@ -35,7 +35,7 @@ jobs:
 
       - name: Install OATS
         env:
-          OATS_VERSION: latest
+          OATS_VERSION: 173ac1f6a190c2ffd156a98dfe923c70a2a0c3ca
         run: go install "github.com/grafana/oats@${OATS_VERSION}"
 
       - name: Run acceptance tests