fix: use local.environment instead of var.environment to avoid null in string template

The tflint validation was failing because var.environment can be null, and null values cannot be included in string templates. Changed to use local.environment which has a fallback value.

Fixes the tflint error: Invalid template interpolation value. The expression result is null.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: npalm

examples/multi-runner/main.tf

@@ -28,7 +28,7 @@ locals {
   aws_region  = var.aws_region
 
   # create map only with amazon linux 2023 x64 and arm64 to overwrite the default
-  al2023_arm64_name = "/${var.environment}/examples/multi-runner/aws-github-runners/ami/amazon-linux-2023-arm64"
+  al2023_arm64_name = "/${local.environment}/examples/multi-runner/aws-github-runners/ami/amazon-linux-2023-arm64"
   ssm_ami_arns = {
     "linux-x64" = data.aws_ssm_parameter.al2023_x64.arn
     # construct the arn to avoid terraform count errors