change the reflect package to an unsafe package (#7143)

- as 'reflect.String.Header' is deprecated, it is replaced with an unsafe package.

Signed-off-by: Youngjun <[email protected]>

pkg/store/cache/inmemory.go

@@ -5,7 +5,6 @@ package storecache
 
 import (
 	"context"
-	"reflect"
 	"sync"
 	"unsafe"
 
@@ -277,12 +276,7 @@ func (c *InMemoryIndexCache) reset() {
 }
 
 func copyString(s string) string {
-	var b []byte
-	h := (*reflect.SliceHeader)(unsafe.Pointer(&b))
-	h.Data = (*reflect.StringHeader)(unsafe.Pointer(&s)).Data
-	h.Len = len(s)
-	h.Cap = len(s)
-	return string(b)
+	return string(unsafe.Slice(unsafe.StringData(s), len(s)))
 }
 
 // copyToKey is required as underlying strings might be mmaped.