[typescript] fix cast problem

Created by: topce

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
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Description of the PR

(details of the change, additional tests that have been done, reference to the issue for tracking, etc) In same cases there is error when generate typescript-angular Exception: io.swagger.v3.oas.models.media.Schema cannot be cast to io.swagger.v3.oas.models.media.NumberSchema at org.openapitools.codegen.DefaultGenerator.processOperation(DefaultGenerator.java:934) at org.openapitools.codegen.DefaultGenerator.processPaths(DefaultGenerator.java:825) at org.openapitools.codegen.DefaultGenerator.generateApis(DefaultGenerator.java:460) at org.openapitools.codegen.DefaultGenerator.generate(DefaultGenerator.java:786) at org.openapitools.codegen.cmd.Generate.run(Generate.java:315) at org.openapitools.codegen.OpenAPIGenerator.main(OpenAPIGenerator.java:58) Caused by: java.lang.ClassCastException: io.swagger.v3.oas.models.media.Schema cannot be cast to io.swagger.v3.oas.models.media.NumberSchema at org.openapitools.codegen.languages.AbstractTypeScriptClientCodegen.toDefaultValue(AbstractTypeScriptClientCodegen.java:328) at org.openapitools.codegen.DefaultCodegen.fromProperty(DefaultCodegen.java:1609) at org.openapitools.codegen.DefaultCodegen.fromParameter(DefaultCodegen.java:2530) at org.openapitools.codegen.DefaultCodegen.fromOperation(DefaultCodegen.java:2221) at org.openapitools.codegen.DefaultGenerator.processOperation(DefaultGenerator.java:902) ... 5 more