ci: set AWS_REGION on Windows image build jobs

The Windows shell runner uses the host docker config, whose ecr-login
credsStore fails `list` with MissingRegion during the anonymous
mcr.microsoft.com base-image pull. Give the helper a region so it stops
erroring, leaving the rest of the host config (incl. ambient
registry.ddbuild.io auth) untouched.

Author: realFlowControl

.gitlab/generate-ci-images.php

@@ -148,6 +148,12 @@ function parse_compose(string $path, array $env): array
   variables:
     DDCI_CONFIGURE_OTEL_EXPORTER: "true"
     GIT_STRATEGY: none
+    # The host docker config uses the ecr-login credsStore; its `list` errors
+    # with MissingRegion (e.g. on the anonymous mcr.microsoft.com base pull).
+    # Give the helper a region so it stops failing; leaves the rest of the
+    # host config (and its ambient registry.ddbuild.io auth) untouched.
+    AWS_REGION: "us-east-1"
+    AWS_DEFAULT_REGION: "us-east-1"
   script: |
     # Kill leftover containers; a previous run may still hold php_ddtrace.dll open.
     $containers = docker ps -aq 2>$null