ci: build musl only for arm64 and reuse toolchain cache [CI]

.woodpecker/linux-agent.yml

@@ -16,18 +16,6 @@ when:
 concurrency: 1
 
 steps:
-  - name: build-musl-amd64
-    image: bash
-    environment:
-      GITEA_BASE: http://127.0.0.1:3100
-      GITEA_TOKEN:
-        from_secret: gitea_token
-      RELEASE_SIGNING_KEY:
-        from_secret: release_signing_key
-    commands:
-      - python3 ci/run-with-timeout.py 3600 bash ci/build-linux-agent.sh linux-musl-x64
-    depends_on: []
-
   - name: build-musl-arm64
     image: bash
     environment: