Removed db schema config from test coverage

refs https://ghost.slack.com/archives/C02G9E68C/p1669707419081529?thread_ts=1669702577.532999&cid=C02G9E68C
refs https://github.com/TryGhost/Toolbox/issues/117

- Database schema definition file is a special type of "configuration" file containing mostly static declarations. This sort of code should not be tested by unit tests, rather by e2e tests

ghost/core/.c8rc.json

@@ -6,10 +6,10 @@
     "text-summary",
     "cobertura"
   ],
-  "statements": 61,
+  "statements": 60,
   "branches": 85,
   "functions": 51,
-  "lines": 61,
+  "lines": 60,
   "include": [
     "core/{*.js,frontend,server,shared}"
   ],
@@ -17,6 +17,7 @@
     "core/frontend/src/**",
     "core/frontend/public/**",
     "core/server/data/migrations/**",
+    "core/server/data/schema/schema.js",
     "!core/server/data/migrations/utils.js",
     "core/frontend/web/**",
     "!core/frontend/web/middleware/**",