The Gitea runner assigns a different workspace directory hash on each
run (e.g. /var/lib/gitea-runner/.cache/act/<hash>/hostexecutor/). When
CCACHE_DIR was set to ${{ github.workspace }}/.ccache, the actions/cache
save and restore operated on a path that changed every run, making the
restored cache land in the wrong location. This caused 0% hit rate on
the second build despite the cache being saved successfully.
Fix by using a fixed path (/tmp/ccache-kindred-create) for CCACHE_DIR
and the cache action path. CCACHE_BASEDIR remains set to the workspace
so ccache stores relative source paths, making cache entries portable
across different workspace directories.
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