Fix Mbed docker image for CI (#10645)

* Remove PW_ENVIRONMENT_ROOT env from mbed docker image

* Bump docker image version
diff --git a/integrations/docker/images/chip-build-mbed-os/Dockerfile b/integrations/docker/images/chip-build-mbed-os/Dockerfile
index c3263ed..cd7724d 100644
--- a/integrations/docker/images/chip-build-mbed-os/Dockerfile
+++ b/integrations/docker/images/chip-build-mbed-os/Dockerfile
@@ -34,6 +34,5 @@
 # ------------------------------------------------------------------------------
 # Configure environment variables
 ENV OPENOCD_PATH=/opt/openocd/
-ENV PW_ENVIRONMENT_ROOT=/home/vscode/pigweed/env
 
 ENV PATH="${PATH}:${OPENOCD_PATH}/bin"
diff --git a/integrations/docker/images/chip-build/version b/integrations/docker/images/chip-build/version
index bca6bd0..7cc5551 100644
--- a/integrations/docker/images/chip-build/version
+++ b/integrations/docker/images/chip-build/version
@@ -1 +1 @@
-0.5.17 Version bump reason: Add for Ameba platform
+0.5.18 Version bump reason: Fix Mbed docker image for CI