fix: disable scan result cache check (#1012)

Update the API to no longer attempt to use cached scan
results.  This is because the feature is not proving useful for
the Notify use case where most attachments are unique.

Additionally during heavy Notify sends, the cache result
lookup is causing database connection exhaustion errors.

terragrunt/aws/api/lambda.tf

@@ -20,6 +20,7 @@ module "scan_files" {
   environment_variables = {
     API_AUTH_TOKEN_SECRET_ARN    = aws_secretsmanager_secret.api_auth_token.id
     AV_DEFINITION_S3_BUCKET      = "${var.product_name}-${var.env}-clamav-defs"
+    AV_SCAN_USE_CACHE            = "False"
     AWS_MAX_ATTEMPTS             = "5"
     AWS_RETRY_MODE               = "standard"
     COMPLETED_SCANS_TABLE_NAME   = "completed-scans"