fix: allow overriding RUNNER_TOOL_CACHE from the config file (#178)

- rc.getToolCache(ctx) is used to figure out RUNNER_TOOL_CACHE and  returns RUNNER_TOOL_CACHE if it is found in the runner config, e.g.
  ```yaml
  container:
    env:
	  RUNNER_TOOL_CACHE: /srv/toolcache
  ```
- store the value in the new `toolCache` data member for containers,  in the same way it is done for host
- GetRunnerContext for containers return `toolCache` instead of a  hard coded string
- add integration test

Closes forgejo/runner#184

Reviewed-on: https://code.forgejo.org/forgejo/act/pulls/178
Reviewed-by: Michael Kriese <michael.kriese@gmx.de>
Co-authored-by: Earl Warren <contact@earl-warren.org>
Co-committed-by: Earl Warren <contact@earl-warren.org>

act/container/linux_container_environment_extensions.go

@@ -10,7 +10,9 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
-type LinuxContainerEnvironmentExtensions struct{}
+type LinuxContainerEnvironmentExtensions struct {
+	toolCache string
+}
 
 // Resolves the equivalent host path inside the container
 // This is required for windows and WSL 2 to translate things like C:\Users\Myproject to /mnt/users/Myproject
@@ -74,12 +76,12 @@ func (*LinuxContainerEnvironmentExtensions) JoinPathVariable(paths ...string) st
 	return strings.Join(paths, ":")
 }
 
-func (*LinuxContainerEnvironmentExtensions) GetRunnerContext(ctx context.Context) map[string]interface{} {
+func (l *LinuxContainerEnvironmentExtensions) GetRunnerContext(ctx context.Context) map[string]interface{} {
 	return map[string]interface{}{
 		"os":         "Linux",
 		"arch":       RunnerArch(ctx),
 		"temp":       "/tmp",
-		"tool_cache": "/opt/hostedtoolcache",
+		"tool_cache": l.toolCache,
 	}
 }