bug: ion-icon [src] binding for string value regression after stencil upgrade

### Prerequisites

- [x] I have read the [Contributing Guidelines](https://github.com/ionic-team/ionic-framework/blob/main/docs/CONTRIBUTING.md#creating-an-issue).
- [x] I agree to follow the [Code of Conduct](https://ionicframework.com/code-of-conduct).
- [x] I have searched for [existing issues](https://github.com/ionic-team/ionic-framework/issues) that already report this problem, without success.

### Ionic Framework Version

v8.x

### Current Behavior

ion-icon using the [src] binding with string value inside a popover without ion-content stopped rendering.

**Notes:**
I know [src]="'value'" is redundant compared to src="value", but it worked fine before the update.

This seems to be a regression since the same Angular + Ionic code works perfectly in 8.7.0 but breaks in 8.7.1.

While ion-content is recommended, I don’t think it’s strictly required, and this issue might reveal another underlying bug.

Example of broken code:

```

```

Example that works:

```

```

### Expected Behavior

ion-icon src should be rendered as before, regarding if string value (url) will be provided using [src]="''" or src=""

### Steps to Reproduce

1. Create a component containing an ion-icon with a custom [src] binding pointing to valid svg url
2. ✅ Display the component inline → works.
3. ✅ Display the component inside a popover with ion-content → works.
4. ❌ Display the component inside a popover without ion-content → icon does not render.

Reproduction repo:
[StackBlitz reproduction](https://stackblitz.com/~/github.com/andrzejpindor/ionic-icon-bindings-regression-repro?file=src/app/app.component.ts)

### Code Reproduction URL

https://stackblitz.com/~/github.com/andrzejpindor/ionic-icon-bindings-regression-repro?file=src/app/foo-ion-content/foo-ion-content.component.html:L9-L11

### Ionic Info

```
Ionic:

Ionic CLI : 7.2.1
Ionic Framework : @ionic/angular 8.7.2
@angular-devkit/build-angular : 19.2.15
@angular-devkit/schematics : 19.2.15
@angular/cli : 19.2.15
@ionic/angular-toolkit : 12.3.0

Utility:

cordova-res : 0.15.4
native-run : 2.0.1

System:

NodeJS : v20.15.1 (/Users/andrzejpindor/.local/share/nvm/v20.15.1/bin/node)
npm : 10.7.0
OS : macOS Unknown
```

### Additional Information

_No response_

Start with the linked StackBlitz reproduction, especially src/app/app.component.ts and src/app/foo-ion-content/foo-ion-content.component.html around lines 9-11. Compare the behavior across Ionic 8.7.0, 8.7.1, and 8.7.2 for inline, ion-content, and content-free popover cases; done means the bound SVG URL renders in all documented cases.

索引モデルが issue の本文から書いたものです。