Preallocate slice in update_test.go

Use make() with a known capacity instead of an empty slice literal,
so the append loop doesn't have to grow the backing array.

Author: JamieMagee

cmd/dependabot/internal/cmd/update_test.go

@@ -191,7 +191,7 @@ func Test_processInput(t *testing.T) {
 			}
 		}
 
-		actualCredentialsMetadataHosts := []string{}
+		actualCredentialsMetadataHosts := make([]string, 0, len(credentialsMetadataHosts))
 		for host := range credentialsMetadataHosts {
 			actualCredentialsMetadataHosts = append(actualCredentialsMetadataHosts, host)
 		}