pkg/settings: use sync.OnceFunc to prevent double close (#1765)

Author: jmank88

pkg/settings/map.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"strconv"
+	"sync"
 
 	"github.com/smartcontractkit/chainlink-common/pkg/contexts"
 )
@@ -102,5 +103,5 @@ func (s *SettingMap[T]) Subscribe(ctx context.Context, registry Registry) (<-cha
 
 	// no-op
 	ch := make(chan Update[T])
-	return ch, func() { close(ch) }
+	return ch, sync.OnceFunc(func() { close(ch) })
 }

pkg/settings/settings.go

@@ -8,6 +8,7 @@ import (
 	"net/url"
 	"reflect"
 	"strconv"
+	"sync"
 	"time"
 
 	"golang.org/x/time/rate"
@@ -236,10 +237,10 @@ func (s *Setting[T]) Subscribe(ctx context.Context, r Registry) (<-chan Update[T
 			}
 		}
 	}()
-	return values, func() {
+	return values, sync.OnceFunc(func() {
 		stop()
 		close(stopped)
-	}
+	})
 }
 
 // InitConfig accepts a pointer to a config struct and iterates over all the fields, initializing any Setting fields