fix: remove artifacts after solcov is run

.solcover.js

@@ -9,6 +9,8 @@ module.exports = {
     await run("typechain");
   },
   onIstanbulComplete: async function (_config) {
+    /* We need to do this because solcover generates bespoke artifacts. */
+    shell.rm("-rf", "./artifacts");
     shell.rm("-rf", "./typechain");
   },
   skipFiles: ["mocks", "test"],