remove spring-milestones

Author: rwinch

.github/dependabot.yml

@@ -16,8 +16,6 @@ updates:
       timezone: "Etc/UTC"
     open-pull-requests-limit: 20
     labels: [ "type: dependency-upgrade" ]
-    registries:
-      - "spring-milestones"
     ignore:
       - dependency-name: "org.junit:junit-bom"
         update-types: [ "version-update:semver-major" ]
@@ -35,8 +33,6 @@ updates:
       timezone: "Etc/UTC"
     open-pull-requests-limit: 20
     labels: [ "type: dependency-upgrade" ]
-    registries:
-      - "spring-milestones"
     ignore:
       - dependency-name: "org.junit:junit-bom"
         update-types: [ "version-update:semver-major" ]