Fix dotenv file associations

Commit f317401 updated dotenv file associations to include files that
begin with `env` instead of `.env`. Dotenv files are sometimes named
`environment.env` or simply `env`, so this was somewhat helpful. However
it also meant that files like `environment.md` would be incorrectly
associated with `dotenv` when they should be associated with `markdown`.
This commit will adjust the syntax to use more specific glob patterns,
with curly braces used to group conditions and reduce code duplication.

https://code.visualstudio.com/docs/editor/glob-patterns
https://code.visualstudio.com/docs/languages/identifiers

vscode/User/settings.json

@@ -41,8 +41,7 @@
     }
   },
   "files.associations": {
-    "**/.env*": "dotenv",
-    "**/env*": "dotenv",
+    "{**/*.env,**/env}": "dotenv",
     "**/*.hujson": "jsonc",
     "**/.zfunc/*": "shellscript"
   },