Make distinct code and console admonitions so readers are less likely to miss them (#20585)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/configuration/conserving_memory.md

@@ -57,7 +57,7 @@ By default, we optimize model inference using CUDA graphs which take up extra me
 
 You can adjust `compilation_config` to achieve a better balance between inference speed and memory usage:
 
-??? Code
+??? code
 
     ```python
     from vllm import LLM
@@ -129,7 +129,7 @@ reduce the size of the processed multi-modal inputs, which in turn saves memory.
 
 Here are some examples:
 
-??? Code
+??? code
 
     ```python
     from vllm import LLM

docs/configuration/env_vars.md

@@ -7,7 +7,7 @@ vLLM uses the following environment variables to configure the system:
 
     All environment variables used by vLLM are prefixed with `VLLM_`. **Special care should be taken for Kubernetes users**: please do not name the service as `vllm`, otherwise environment variables set by Kubernetes might conflict with vLLM's environment variables, because [Kubernetes sets environment variables for each service with the capitalized service name as the prefix](https://kubernetes.io/docs/concepts/services-networking/service/#environment-variables).
 
-??? Code
+??? code
 
     ```python
     --8<-- "vllm/envs.py:env-vars-definition"