millicpu allowed to be higher then overwriteMaxAllowed

Summary

In !874 (merged) introduced a new configuration to the user tho set cpu_limit_overwrite_max_allowed and cpu_request_overwrite_max_allowed however when use the millicpu values for example 100m this doesn't work and the user can set a higher value. Also, the error returned when it's an invalid is confusing with the resource "MemoryLimit" requested by the build "4Gi" does not match or is less than limit allowed "512Mi" is not "less" but it should be "higher"

Steps to reproduce

Configure a Kubernetes Runner with the same overwrites set below.
Run the .gitlab-ci.yml below

.gitlab-ci.yml

variables:
  IMAGE: alpine:3.11
  
job:
  variables:
    KUBERNETES_CPU_REQUEST: 400m
    KUBERNETES_CPU_LIMIT: 600m
    KUBERNETES_MEMORY_REQUEST: 500Mi
    KUBERNETES_MEMORY_LIMIT: 4Gi
  image: ${IMAGE}
  script:
  - echo -n "things are breaking"

Actual behavior

CPU limit is set, even though it's higher than max. Error messing regarding memory is confusing requested by the build "4Gi" does not match or is less than limit allowed "512Mi"

Expected behavior

Job failed during setting CPU limits since we set the CPU LIMIT to be 600m but the max CPU limit that is allowed is 400m

Relevant logs and/or screenshots

job log

 Running with gitlab-runner 13.0.0~beta.169.gdccb3f31 (dccb3f31)
   on test-gitlab-runner-669f8c894c-pdtsr _fDJFULD
Preparing the "kubernetes" executor
00:09
 "CPULimit" overwritten with "600m"                   <-------- Should not be set
 "CPURequest" overwritten with "400m"
 ERROR: Preparation failed: couldn't prepare overwrites: the resource "MemoryLimit" requested by the build "4Gi" does not match or is less than limit allowed "512Mi"           <--- Confusing error message because of "is less" when we mean "higher"
 Will be retried in 3s ...
 "CPULimit" overwritten with "600m"
 "CPURequest" overwritten with "400m"
 ERROR: Preparation failed: couldn't prepare overwrites: the resource "MemoryLimit" requested by the build "4Gi" does not match or is less than limit allowed "512Mi"
 Will be retried in 3s ...
 "CPULimit" overwritten with "600m"
 "CPURequest" overwritten with "400m"
 ERROR: Preparation failed: couldn't prepare overwrites: the resource "MemoryLimit" requested by the build "4Gi" does not match or is less than limit allowed "512Mi"
 Will be retried in 3s ...
 ERROR: Job failed (system failure): couldn't prepare overwrites: the resource "MemoryLimit" requested by the build "4Gi" does not match or is less than limit allowed "512Mi"

Environment description

config.toml contents

[[runners]]
  name = "kubernetes"
  url = "http://192.168.144.160:3000"
  token = "xxxx"
  executor = "kubernetes"
  [runners.kubernetes]
    image = "alpine:3.11"
    privileged = true
    bearer_token = ""
    namespace = "default"
    namespace_overwrite_allowed = ""
    cpu_limit = "200m"
    cpu_limit_overwrite_max_allowed = "400m"
    memory_limit = "256Mi"
    memory_limit_overwrite_max_allowed = "512Mi"
    cpu_request = "100m"
    cpu_request_overwrite_max_allowed = "200m"
    memory_request = "128Mi"
    memory_request_overwrite_max_allowed = "256Mi"
    poll_timeout = 180

Used GitLab Runner version

12.9

Possible fixes

Instead of use .Value to compare the two resources use .Cmp because .Value always returns 1 when it's set to millicpus