fix: remove unused volumen mount

.woodpecker/update-package-index-ubuntu-2404-arm64.yaml

@@ -30,8 +30,6 @@ steps:
       # set the location of the 'pkgcache' cache dir which persists the R package dependencies needed to install the packages themselves
       R_PKG_CACHE_DIR: /mnt/cache/pkgcache
       R_LIBS_USER: /mnt/cache/R-pkgs
-    volumes:
-      - arm64-binaries-r-dep-cache-ubuntu-2404:/mnt/cache
     commands:
       - git clone -q https://pat-s:$$GIT_RO_TOKEN@git.devxy.io/devxy/build-binaries.git .
       - rm -rf /mnt/cache/packages/*