[BUG] Make delay writer actually work

- Reading the code of this delay writer implemenation, it looks like
that it should only actually write content to the `io.Writer` if x
amount of time has passed by. However in practice it was always printing
the buffer even if the X amount of time didn't pass yet. This is in line
with what was being said in the issue that this was to help with
https://github.com/go-gitea/gitea/issues/9610.
- This was caused by the extra `Close()` calls which in turn caused that
when the second `Close` is called (which is done in a defer already) it
would've printed the buffer anyway. So remove the extra calls to `Close()`.
- Add unit test.

(cherry picked from commit 9320ffd2b5)

cmd/hook.go

@@ -347,11 +347,10 @@ Forgejo or set your environment appropriately.`, "")
 	}
 
 	var out io.Writer
-	var dWriter *delayWriter
 	out = &nilWriter{}
 	if setting.Git.VerbosePush {
 		if setting.Git.VerbosePushDelay > 0 {
-			dWriter = newDelayWriter(os.Stdout, setting.Git.VerbosePushDelay)
+			dWriter := newDelayWriter(os.Stdout, setting.Git.VerbosePushDelay)
 			defer dWriter.Close()
 			out = dWriter
 		} else {
@@ -414,7 +413,6 @@ Forgejo or set your environment appropriately.`, "")
 			hookOptions.RefFullNames = refFullNames
 			resp, extra := private.HookPostReceive(ctx, repoUser, repoName, hookOptions)
 			if extra.HasError() {
-				_ = dWriter.Close()
 				hookPrintResults(results)
 				return fail(ctx, extra.UserMsg, "HookPostReceive failed: %v", extra.Error)
 			}
@@ -434,7 +432,6 @@ Forgejo or set your environment appropriately.`, "")
 		}
 		fmt.Fprintf(out, "Processed %d references in total\n", total)
 
-		_ = dWriter.Close()
 		hookPrintResults(results)
 		return nil
 	}
@@ -447,7 +444,6 @@ Forgejo or set your environment appropriately.`, "")
 
 	resp, extra := private.HookPostReceive(ctx, repoUser, repoName, hookOptions)
 	if resp == nil {
-		_ = dWriter.Close()
 		hookPrintResults(results)
 		return fail(ctx, extra.UserMsg, "HookPostReceive failed: %v", extra.Error)
 	}
@@ -463,9 +459,8 @@ Forgejo or set your environment appropriately.`, "")
 			return fail(ctx, extra.UserMsg, "SetDefaultBranch failed: %v", extra.Error)
 		}
 	}
-	_ = dWriter.Close()
-	hookPrintResults(results)
 
+	hookPrintResults(results)
 	return nil
 }