roachtest: deflake azure backup fixture roachtest

I suspect our azure external storage reader doesn't currently retry read
timeouts. This patch disables the timeout to see if that deflakes the test.

Informs #155427

Release note: none

Author: msbutler

pkg/cmd/roachtest/tests/backup_fixtures.go

@@ -195,6 +195,7 @@ func (bd *backupDriver) prepareCluster(ctx context.Context) {
 				"kv.snapshot_rebalance.max_rate":                    "256 MiB",
 				"server.debug.default_vmodule":                      "s3_storage=2",
 				"cloudstorage.s3.client_retry_token_bucket.enabled": "false",
+				"cloudstorage.azure.try.timeout":                    "0s",
 			},
 			install.EnvOption{
 				fmt.Sprintf("COCKROACH_AZURE_APPLICATION_CREDENTIALS_FILE=%s", azureCredentialsFilePath),