chore: pin Dockerfile to node:24.15.0-alpine to match repo convention

Author: KARSE22

actions/contract_tests/Dockerfile

@@ -1,4 +1,4 @@
-FROM node:24-alpine
+FROM node:24.15.0-alpine
 
 # Copy code file from action repository to "/" in the container
 COPY entrypoint.sh /entrypoint.sh