Add possibility to not create ebs (#1807)

Co-authored-by: Grzegorz Cwiklinski <[email protected]@smartpension.co.uk>

Author: Hankier

Diff for: modules/runners/main.tf

@@ -55,7 +55,7 @@ resource "aws_launch_template" "runner" {
   name = "${var.environment}-action-runner"
 
   dynamic "block_device_mappings" {
-    for_each = [var.block_device_mappings]
+    for_each = var.block_device_mappings != null ? [var.block_device_mappings] : []
     content {
       device_name = lookup(block_device_mappings.value, "device_name", "/dev/xvda")