fix: allow relocating the tool cache and mounting over runner paths (#1122)

1. Docker rejects two mounts on one target, so a `container.volumes:` or `--volume` aimed at `/opt/hostedtoolcache` failed the job with `Duplicate mount point`. Job and service volumes now displace the mount on the same path, and `name:/target:ro` no longer mounts read-write at the literal path `/target:ro`.
1. Setting `RUNNER_TOOL_CACHE` only changed what the variable said, the cache stayed where it was, so tools writing to it landed outside the mount and `${{ runner.tool_cache }}` disagreed with the variable. It now relocates the cache. Leaving it unset behaves as before.
1. Unknown `config.yaml` keys now warn instead of being dropped without a trace.

Fixes https://gitea.com/gitea/runner/issues/813

---------

Co-authored-by: bircni <bircni@icloud.com>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1122
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

act/container/docker_run_test.go

@@ -23,6 +23,7 @@ import (
 	cerrdefs "github.com/containerd/errdefs"
 	"github.com/moby/moby/api/pkg/stdcopy"
 	"github.com/moby/moby/api/types/container"
+	"github.com/moby/moby/api/types/mount"
 	mobyclient "github.com/moby/moby/client"
 	"github.com/sirupsen/logrus/hooks/test"
 	"github.com/stretchr/testify/assert"
@@ -660,3 +661,22 @@ func TestCheckVolumesRejectsEscapingHostPaths(t *testing.T) {
 	})
 	assert.Empty(t, hostConf.Binds)
 }
+
+func TestMergeContainerConfigsVolumesReplaceRunnerMounts(t *testing.T) {
+	logger, _ := test.NewNullLogger()
+	ctx := common.WithLogger(context.Background(), logger)
+	cr := &containerReference{
+		input: &NewContainerInput{
+			NetworkMode: "bridge",
+			Options:     "--volume /host/tools:/opt/hostedtoolcache",
+		},
+	}
+
+	_, hostConf, err := cr.mergeContainerConfigs(ctx, &container.Config{}, &container.HostConfig{
+		Binds:  []string{"/var/run/docker.sock:/var/run/docker.sock"},
+		Mounts: []mount.Mount{{Type: mount.TypeVolume, Source: "act-toolcache", Target: "/opt/hostedtoolcache"}},
+	})
+	require.NoError(t, err)
+	assert.Equal(t, []string{"/var/run/docker.sock:/var/run/docker.sock", "/host/tools:/opt/hostedtoolcache"}, hostConf.Binds)
+	assert.Empty(t, hostConf.Mounts)
+}