chore: enable usestdlibvars linter

Signed-off-by: Matthieu MOREL <matthieu.morel35@gmail.com>

Author: mmorel-35

.golangci.yml

@@ -11,6 +11,7 @@ linters:
     - gocritic
     - misspell
     - testifylint
+    - usestdlibvars
 
   settings:
     errcheck:

providers/prometheus/server_test.go

@@ -175,7 +175,7 @@ func (s *ServerInterceptorTestSuite) TestContextCancelledTreatedAsStatus() {
 // Order of matching label vales does not matter.
 func fetchPrometheusLines(t *testing.T, reg prometheus.Gatherer, metricName string, matchingLabelValues ...string) []string {
 	resp := httptest.NewRecorder()
-	req, err := http.NewRequest("GET", "/", http.NoBody)
+	req, err := http.NewRequest(http.MethodGet, "/", http.NoBody)
 	require.NoError(t, err, "failed creating request for Prometheus handler")
 
 	promhttp.HandlerFor(reg, promhttp.HandlerOpts{}).ServeHTTP(resp, req)