fix(healthcheck): prevent race condition on the healthchecker (#3400)

Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Co-authored-by: Quentin McGaw <quentin.mcgaw@gmail.com>

Thanks also to @arturhoo for also trying to resolve this issue in #3410

internal/healthcheck/checker.go

@@ -8,7 +8,6 @@ import (
 	"net"
 	"net/netip"
 	"strings"
-	"sync"
 	"time"
 
 	"github.com/qdm12/gluetun/internal/healthcheck/dns"
@@ -24,7 +23,6 @@ type Checker struct {
 	icmpTargetIPs  []netip.Addr
 	smallCheckType string
 	startupOnFail  bool
-	configMutex    sync.Mutex
 
 	icmpNotPermitted *bool
 
@@ -55,8 +53,6 @@ func NewChecker(logger Logger) *Checker {
 func (c *Checker) SetConfig(tlsDialAddrs []string, icmpTargets []netip.Addr,
 	smallCheckType string, startupOnFail bool,
 ) {
-	c.configMutex.Lock()
-	defer c.configMutex.Unlock()
 	c.tlsDialAddrs = tlsDialAddrs
 	c.icmpTargetIPs = icmpTargets
 	c.smallCheckType = smallCheckType
@@ -166,10 +162,8 @@ func (c *Checker) Stop() error {
 }
 
 func (c *Checker) smallPeriodicCheck(ctx context.Context) error {
-	c.configMutex.Lock()
 	icmpTargetIPs := make([]netip.Addr, len(c.icmpTargetIPs))
 	copy(icmpTargetIPs, c.icmpTargetIPs)
-	c.configMutex.Unlock()
 	tryTimeouts := []time.Duration{
 		5 * time.Second,
 		5 * time.Second,