Enable some linters (#3129)

Mostly those that did not require much work.

From #2960

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

cmd/agent/agent.go

@@ -271,6 +271,8 @@ func getBackendEngine(backendCtx context.Context, backendName string, addons []s
 }
 
 func runWithRetry(context *cli.Context) error {
+	initHealth()
+
 	retryCount := context.Int("connect-retry-count")
 	retryDelay := context.Duration("connect-retry-delay")
 	var err error

cmd/agent/health.go

@@ -31,7 +31,7 @@ import (
 // following specification:
 //   https://github.com/mozilla-services/Dockerflow
 
-func init() {
+func initHealth() {
 	http.HandleFunc("/varz", handleStats)
 	http.HandleFunc("/healthz", handleHeartbeat)
 	http.HandleFunc("/version", handleVersion)
@@ -48,10 +48,13 @@ func handleHeartbeat(w http.ResponseWriter, _ *http.Request) {
 func handleVersion(w http.ResponseWriter, _ *http.Request) {
 	w.WriteHeader(200)
 	w.Header().Add("Content-Type", "text/json")
-	_ = json.NewEncoder(w).Encode(versionResp{
+	err := json.NewEncoder(w).Encode(versionResp{
 		Source:  "https://github.com/woodpecker-ci/woodpecker",
 		Version: version.String(),
 	})
+	if err != nil {
+		log.Error().Err(err).Msg("handleVersion")
+	}
 }
 
 func handleStats(w http.ResponseWriter, _ *http.Request) {