[BUG]: (NotFound) while fetching schema

## What's wrong?

Running `dab validate` fails to download our schema.

## What happened?

```sh
C:\Temp\dab-harness>dab validate -c dab-config.json
Information: Microsoft.DataApiBuilder 1.5.56
Information: User provided config file: dab-config.json
Information: Validating config file: dab-config.json
Loading config file from C:\Temp\dab-harness\dab-config.json.
Warning: Received response: (NotFound) while fetching schema from url: https://github.com/Azure/data-api-builder/releases/download/v1.5.56/dab.draft.schema.json
Information: The config satisfies the schema requirements.
Information: Validating entity relationships.
Information: Config is valid.
```

Not quite sure how this is only a warning. But it should not occur at all.

## Version

```sh
C:\Temp\dab-harness>dab --version
Microsoft.DataApiBuilder 1.5.56+61c726a0fc38ab5a1d9e52cc3593bbd2a8633aec
```

## Configuration

```sh
C:\Temp\dab-harness>cd "c:\Temp\dab-harness" && dab init --database-type mssql --connection-string "@env('MSSQL_CONNECTION_STRING')" --host-mode development --rest.enabled true --graphql.enabled true --auth.provider StaticWebApps -c "dab-config.json"
Information: Microsoft.DataApiBuilder 1.5.56
Information: Generating user provided config file with name: dab-config.json
Information: Config file generated.
Information: SUGGESTION: Use 'dab add [entity-name] [options]' to add new entities in your config.

c:\Temp\dab-harness>cd "c:\Temp\dab-harness" && dab configure --runtime.cache.enabled true -c "dab-config.json"
Information: Microsoft.DataApiBuilder 1.5.56
Information: User provided config file: dab-config.json
Loading config file from c:\Temp\dab-harness\dab-config.json.
Information: Updated RuntimeConfig with Runtime.Cache.Enabled as 'True'
Information: Successfully updated runtime settings in the config file.
```
```json
{
"$schema": "https://github.com/Azure/data-api-builder/releases/download/v1.5.56/dab.draft.schema.json",
"data-source": {
"database-type": "mssql",
"connection-string": "@env('MSSQL_CONNECTION_STRING')"
},
"runtime": {
"rest": {
"enabled": true,
"path": "/api",
"request-body-strict": true
},
"graphql": {
"enabled": true,
"path": "/graphql",
"allow-introspection": true
},
"host": {
"cors": {
"origins": [],
"allow-credentials": false
},
"authentication": {
"provider": "StaticWebApps"
},
"mode": "development"
},
"cache": {
"enabled": true
}
},
"entities": {}
}
```

示されている `dab validate -c dab-config.json` コマンドと設定で失敗を再現し、その後、出力に報告されているスキーマ URL と取得動作を追跡します。v1.5.56 のスキーマ URL が NotFound を返す理由を確認します。完了の条件は、バリデーションでこの警告が出なくなり、スキーマが取得されるか、失敗が意図どおりに処理されることです。

索引モデルが issue の本文から書いたものです。