adds *.t.err to file associations (vercel#8920)

When you run integrations tests and there's an error it creates *.t.err
files in the cram format. With this file association added, now those
files will be correctly associated and therefore get syntax highlighting
and all that good stuff.

.vscode/settings.json

@@ -9,7 +9,8 @@
   "debug.javascript.unmapMissingSources": true,
   "files.associations": {
     "libturbo.h": "c",
-    "turbo.json": "jsonc"
+    "turbo.json": "jsonc",
+    "*.t.err": "cram"
   },
   "[cram]": {
     "editor.trimAutoWhitespace": false,