fix(buildifier_availability): specify lint mode to override default

[mattnworb]

buildifer allows you to configure defaults by placing a .buildifer.json file at the root of the project.

If this file happens to have

{
  "lint": "fix",
  ...
}

then the extension will run into an error at startup which presents a confusing "Failed to find a Bazel workspace" error dialog to the user. From the Extension Host logs in the Output panel:

2025-11-24 14:49:33.178 [error] Error: Command failed: buildifier --format=json --mode=check
buildifier: --lint=fix is only compatible with --mode=fix

	at genericNodeError (node:internal/errors:983:15)
	at wrappedFn (node:internal/errors:537:14)
	at ChildProcess.exithandler (node:child_process:418:12)
	at ChildProcess.emit (node:events:519:28)
	at maybeClose (node:internal/child_process:1101:16)
	at Socket.<anonymous> (node:internal/child_process:456:11)
	at Socket.emit (node:events:519:28)
	at Pipe.<anonymous> (node:net:346:12)

since the command in buildifer_availability is just to check that buildifier is present and able to return JSON output, the default from the config file can be overridden to prevent this error.