chore: build with Go 1.26; use Go 1.25 features (#10570)

WaitGroup.Go and built-in gomaxprocs handling.

Signed-off-by: Jakob Borg <jakob@kastelo.net>

cmd/dev/stvanity/main.go

@@ -26,7 +26,6 @@ import (
 	"sync/atomic"
 	"time"
 
-	_ "github.com/syncthing/syncthing/lib/automaxprocs"
 	"github.com/syncthing/syncthing/lib/protocol"
 )
 
@@ -53,11 +52,9 @@ func main() {
 	// Run one certificate generator per CPU core.
 	var wg sync.WaitGroup
 	for i := 0; i < runtime.GOMAXPROCS(-1); i++ {
-		wg.Add(1)
-		go func() {
+		wg.Go(func() {
 			generatePrefixed(prefix, &count, found, stop)
-			wg.Done()
-		}()
+		})
 	}
 
 	// Save the result, when one has been found.