.travis.yml: change arch for Docker build to arm64 (ethereum#31096)

This is an attempt to work around a gcc issue in the Docker build.

Author: fjl

.travis.yml

@@ -13,7 +13,7 @@ jobs:
     - stage: build
       if: type = push
       os: linux
-      arch: amd64
+      arch: arm64
       dist: focal
       go: 1.23.x
       env: