bug: large title appearing on top of modal during navigation transition

# Bug Report

**Ionic version:**
[ ] **4.x**
[x] **5.x**

**Current behavior:**
Navigating while having a Modal open will show the `ion-header` animation

**Expected behavior:**
`ion-header` animation should not be visible when a Modal is open

**Steps to reproduce:**
**Related code:**

https://github.com/NunoSav/ionic-vue-bugs

Steps to reproduce:
1. Open app
2. Click "Go to Page 2"
3. Click "Show Modal"
4. Click "Click here!" (animation will be visible when you click)

**Ionic info:**

```
Ionic:

Ionic CLI : 6.12.2 (/Users/nur/.config/yarn/global/node_modules/@ionic/cli)
Ionic Framework : @ionic/vue 5.5.3

Capacitor:

Capacitor CLI : 2.4.6
@capacitor/core : 2.4.6

Utility:

cordova-res (update available: 0.15.3) : 0.15.1
native-run (update available: 1.3.0) : 1.2.1

System:

NodeJS : v12.16.3 (/usr/local/bin/node)
npm : 6.14.4
OS : macOS Big Sur
```

Start with the linked ionic-vue-bugs reproduction app and follow the listed navigation steps: open Page 2, show the modal, and click “Click here!”. Confirm the fix by ensuring the ion-header animation is not visible while the modal is open during navigation.

由索引模型根据 Issue 内容生成。