fix: fix DataSourceQualifier (#238)

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##### Checklist
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- [ ] `npm test` passes
- [ ] tests and/or benchmarks are included
- [ ] documentation is changed or added
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##### Description of change
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<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit

- **Refactor**
- Simplified the function call in the `DataSourceQualifier`, enhancing
clarity and maintainability.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

core/dal-decorator/src/decorator/DataSourceQualifier.ts

@@ -1,10 +1,8 @@
 import { DataSourceQualifierAttribute } from '@eggjs/tegg-types';
-import type { EggProtoImplClass } from '@eggjs/tegg-types';
 import { QualifierUtil } from '@eggjs/core-decorator';
 
 export function DataSourceQualifier(dataSourceName: string) {
   return function(target: any, propertyKey: PropertyKey, parameterIndex?: number) {
-    QualifierUtil.addInjectQualifier(target.constructor as EggProtoImplClass,
-      propertyKey, parameterIndex, DataSourceQualifierAttribute, dataSourceName);
+    QualifierUtil.addInjectQualifier(target, propertyKey, parameterIndex, DataSourceQualifierAttribute, dataSourceName);
   };
 }