Use only one scrapeMetrics object per test. (#13051)

The scrape loop and scrape cache should use the same instance.
This brings the tests' behavior more in line with production.

Signed-off-by: Paulin Todev <paulin.todev@gmail.com>

scrape/scrape_test.go

@@ -794,6 +794,7 @@ func TestScrapeLoopRun(t *testing.T) {
 
 		scraper       = &testScraper{}
 		app           = func(ctx context.Context) storage.Appender { return &nopAppender{} }
+		scrapeMetrics = newTestScrapeMetrics(t)
 	)
 
 	ctx, cancel := context.WithCancel(context.Background())
@@ -817,7 +818,7 @@ func TestScrapeLoopRun(t *testing.T) {
 		false,
 		nil,
 		false,
-		newTestScrapeMetrics(t),
+		scrapeMetrics,
 	)
 
 	// The loop must terminate during the initial offset if the context
@@ -876,7 +877,7 @@ func TestScrapeLoopRun(t *testing.T) {
 		false,
 		nil,
 		false,
-		newTestScrapeMetrics(t),
+		scrapeMetrics,
 	)
 
 	go func() {
@@ -976,7 +977,8 @@ func TestScrapeLoopMetadata(t *testing.T) {
 	var (
 		signal        = make(chan struct{})
 		scraper       = &testScraper{}
-		cache   = newScrapeCache(newTestScrapeMetrics(t))
+		scrapeMetrics = newTestScrapeMetrics(t)
+		cache         = newScrapeCache(scrapeMetrics)
 	)
 	defer close(signal)
 
@@ -1001,7 +1003,7 @@ func TestScrapeLoopMetadata(t *testing.T) {
 		false,
 		nil,
 		false,
-		newTestScrapeMetrics(t),
+		scrapeMetrics,
 	)
 	defer cancel()