Update Ruby base image and pin Alpine version

.gitlab/ci/.gbpt-base.yml

 .sitespeed-base:
-  image: ruby:3-alpine
+  image: ruby:3-alpine3.21
   before_script:
-    - apk add --no-cache build-base curl
+    - apk add --no-cache build-base curl linux-headers
     - gem install bundler && bundle config without dev && bundle install
 
 .sitespeed-test-base:
   extends: .sitespeed-base
   services:
-    - docker:24.0.6-dind
+    - docker:27-dind
   variables:
     DOCKER_DRIVER: overlay2
     DOCKER_HOST: tcp://docker:2375

.gitlab/ci/sitespeed.yml

@@ -5,9 +5,9 @@ check:sitespeed:
   stage: check
   image: docker:git
   services:
-    - docker:24.0.6-dind
+    - docker:27-dind
   variables:
-    SITESPEED_IMAGE: sitespeedio/sitespeed.io
+    SITESPEED_IMAGE: sitespeedio/sitespeed.io:35
   script:
     - apk add npm
     - npm install --prefix ./sitespeed/plugin/
@@ -22,9 +22,9 @@ check:sitespeed:
 
 check:rubocop:
   stage: check
-  image: ruby:3-alpine
+  image: ruby:3-alpine3.21
   before_script:
-    - apk add build-base
+    - apk add build-base linux-headers
     - gem install bundler && bundle config without run && bundle install
   script:
     - rubocop --parallel
@@ -79,7 +79,7 @@ sitespeed-performance:
   stage: sitespeed
   extends: .sitespeed-test-base
   variables:
-    SITESPEED_IMAGE: sitespeedio/sitespeed.io
+    SITESPEED_IMAGE: sitespeedio/sitespeed.io:35
   script:
     - apk add docker npm
     - npm install --prefix ./sitespeed/plugin/