all: Modernize error wrapping (#8491)

This replaces old style errors.Wrap with modern fmt.Errorf and removes
the (direct) dependency on github.com/pkg/errors. A couple of cases are
adjusted by hand as previously errors.Wrap(nil, ...) would return nil,
which is not what fmt.Errorf does.

lib/model/folder.go

@@ -8,6 +8,7 @@ package model
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"math/rand"
 	"path/filepath"
@@ -15,8 +16,6 @@ import (
 	"sync/atomic"
 	"time"
 
-	"github.com/pkg/errors"
-
 	"github.com/syncthing/syncthing/lib/config"
 	"github.com/syncthing/syncthing/lib/db"
 	"github.com/syncthing/syncthing/lib/events"
@@ -317,7 +316,7 @@ func (f *folder) getHealthErrorAndLoadIgnores() error {
 	}
 	if f.Type != config.FolderTypeReceiveEncrypted {
 		if err := f.ignores.Load(".stignore"); err != nil && !fs.IsNotExist(err) {
-			return errors.Wrap(err, "loading ignores")
+			return fmt.Errorf("loading ignores: %w", err)
 		}
 	}
 	return nil
@@ -1060,6 +1059,7 @@ func (f *folder) monitorWatch(ctx context.Context) {
 				l.Warnf("Filesystem watching (kqueue) is enabled on %v with a lot of files/directories, and that requires a lot of resources and might slow down your system significantly", f.Description())
 			}
 		case <-ctx.Done():
+			aggrCancel() // for good measure and keeping the linters happy
 			return
 		}
 	}