BUILDKIT_SYNTAX should not be flagged as an unrecognized ARG

[rcjsuen]

target "foo" {
  tags = ["myapp"]
  args = {
    BUILDKIT_SYNTAX = "docker/dockerfile:1.0"
  }
}

We should be able to fix this by adding BUIDLKIT_SYNTAX to the list.

docker-language-server/internal/bake/hcl/diagnosticsCollector.go

Lines 26 to 38 in 0884804

	var builtinArgs = []string{
	"HTTP_PROXY",
	"HTTPS_PROXY",
	"FTP_PROXY",
	"ALL_PROXY",
	"NO_PROXY",
	"BUILDKIT_CACHE_MOUNT_NS",
	"BUILDKIT_MULTI_PLATFORM",
	"BUILDKIT_SANDBOX_HOSTNAME",
	"BUILDKIT_DOCKERFILE_CHECK",
	"BUILDKIT_CONTEXT_KEEP_GIT_DIR",
	"SOURCE_DATE_EPOCH",
	}