Pin woodpecker docker images

.woodpecker.yaml

@@ -1,17 +1,16 @@
 variables:
-  - &node_image 'node:20-alpine'
   - &create_synapse_access_token >-
     echo '{"user_id":"ci-dummy","access_token":"ci-dummy","home_server":"ci-dummy","device_id":"ci-dummy"}' > src/config/synapse_access_token.json
 
 steps:
   lint-markdown:
-    image: markdownlint/markdownlint:latest
+    image: markdownlint/markdownlint:0.12.0
     group: test
     commands:
       - mdl .
 
   check-pre-commit:
-    image: python:latest
+    image: python:3.11.5
     group: test
     environment:
       - SKIP=no-commit-to-branch # Ignore "don't commit to protected branch" check
@@ -20,30 +19,30 @@ steps:
       - pre-commit run --all-files
 
   node-install-dependencies:
-    image: *node_image
+    image: node:20.5.1-alpine3.18
     commands:
       - npm clean-install
 
   node-lint:
-    image: *node_image
+    image: node:20.5.1-alpine3.18
     group: test
     commands:
       - npm run lint
 
   node-format:
-    image: *node_image
+    image: node:20.5.1-alpine3.18
     group: test
     commands:
       - npm run format
 
   node-test:
-    image: *node_image
+    image: node:20.5.1-alpine3.18
     commands:
       - *create_synapse_access_token
       - npm test --ci
 
   node-compile:
-    image: *node_image
+    image: node:20.5.1-alpine3.18
     commands:
       - *create_synapse_access_token
       - npm run compile