Verify runner s3 authenticationtype deprecation

data/deprecations/ runner-s3-authenticationtype-nonexplicit-config-deprecation.yml

+- name: "`AuthenticationType` for `[runners.cache.s3]` must be explicitly assigned"
+  announcement_milestone: "14.5" # The milestone when this feature was first announced as deprecated.
+  announcement_date: "2021-11-22"
+  removal_milestone: "15.0" # the milestone when this feature is planned to be removed
+  body: | # Do not modify this line, instead modify the lines below.
+    In GitLab 15.0 and later, to access the AWS S3 cache, you must specify the `AuthenticationType` for [`[runners.cache.s3]`](https://docs.gitlab.com/runner/configuration/advanced-configuration.html#the-runnerscaches3-section). The `AuthenticationType` must be `IAM` or `credentials`.
+
+    Prior to 14.5, if you did not define the `AuthenticationType`, GitLab Runner chose a type for you. 
+  stage: Verify
+  tiers: [Core, Premium, Ultimate]
+  issue_url: https://gitlab.com/gitlab-org/gitlab-runner/-/issues/28171
+  documentation_url: https://docs.gitlab.com/runner/configuration/advanced-configuration.html#the-runnerscaches3-section

doc/update/deprecations.md

@@ -99,6 +99,14 @@ When checking if a runner is "paused", API users are advised to check the boolea
 
 Announced: 
 
+### `AuthenticationType` for `[runners.cache.s3]` must be explicitly assigned
+
+In GitLab 15.0 and later, to access the AWS S3 cache, you must specify the `AuthenticationType` for [`[runners.cache.s3]`](https://docs.gitlab.com/runner/configuration/advanced-configuration.html#the-runnerscaches3-section). The `AuthenticationType` must be `IAM` or `credentials`.
+
+Prior to 14.5, if you did not define the `AuthenticationType`, GitLab Runner chose a type for you. 
+
+Announced: 2021-11-22
+
 ## 15.2
 
 ### NFS for Git repository storage deprecated