Fixed syntax for "and" conditions (#2869)

Fixes a deployment error.

```
<(.Values.monitor.create) and (.Values.monitor.grafana.create)>: can't give argument to non-function .Values.monitor.create
```

We have confirmed that both helm2[1] and helm3[2] work.

[1]: https://v2.helm.sh/docs/chart_template_guide/#operators-are-functions
[2]: https://helm.sh/docs/chart_template_guide/function_list/#and

Co-authored-by: DanielZhangQD <36026334+DanielZhangQD@users.noreply.github.com>
Co-authored-by: Yecheng Fu <fuyecheng@pingcap.com>

charts/tidb-cluster/templates/monitor-secret.yaml

@@ -1,4 +1,4 @@
-{{- if (.Values.monitor.create) and (.Values.monitor.grafana.create) }}
+{{- if and .Values.monitor.create .Values.monitor.grafana.create }}
 apiVersion: v1
 kind: Secret
 metadata: