`az containerapp up --registry-server` fails when ACR has ABAC enabled

### Describe the bug

Same as https://github.com/microsoft/GitHub-Copilot-for-Azure/pull/1106

### Related command

`az containerapp up --name myapp --source myapp --registry-server myacr.azurecr.io`

### Errors

```
The behavior of this command has been altered by the following extension: containerapp
Adding external ingress port 8080 based on dockerfile expose.
Using resource group 'myrg'
Using ContainerAppEnvironment 'mycae' in resource group myrg
Dockerfile detected. Running the build through ACR.
2026/03/26 01:08:46 Downloading source code...
2026/03/26 01:08:48 Finished downloading source code
when specifying push, at least one credential is required

Run ID: cr4 failed after 3s. Error: failed during run, err: exit status 1
Run failed
```

### Issue script & Debug output

[debug.txt](https://github.com/user-attachments/files/26257684/debug.txt)

### Expected behavior

Builds and pushes to the registry, then deploys

### Environment Summary

```
azure-cli 2.84.0

core 2.84.0
telemetry 1.1.0

Extensions:
containerapp 1.3.0b4

Dependencies:
msal 1.35.0b1
azure-mgmt-resource 24.0.0

Python location '/opt/az/bin/python3'
Config directory '/home/node/.azure'
Extensions directory '/home/node/.azure/cliextensions'

Python (Linux) 3.13.11 (main, Feb 25 2026, 02:29:30) [GCC 12.2.0]

Legal docs and information: aka.ms/AzureCliLegal

Your CLI is up-to-date.
```

### Additional context

Debug log is sanitised, except for correlation IDs