Fix Java exception when using Apex client generator

[wing328]

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• 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

To fix the Java exception (casting) when using Apex client generator:

  Exception: io.swagger.v3.oas.models.media.Schema cannot be cast to io.swagger.v3.oas.models.media.BooleanSchema
	at org.openapitools.codegen.DefaultGenerator.processOperation(DefaultGenerator.java:996)
	at org.openapitools.codegen.DefaultGenerator.processPaths(DefaultGenerator.java:891)
	at org.openapitools.codegen.DefaultGenerator.generateApis(DefaultGenerator.java:489)
	at org.openapitools.codegen.DefaultGenerator.generate(DefaultGenerator.java:848)
	at org.openapitools.codegen.cmd.Generate.run(Generate.java:349)
	at org.openapitools.codegen.OpenAPIGenerator.main(OpenAPIGenerator.java:62)
Caused by: java.lang.ClassCastException: io.swagger.v3.oas.models.media.Schema cannot be cast to io.swagger.v3.oas.models.media.BooleanSchema
	at org.openapitools.codegen.languages.ApexClientCodegen.toDefaultValue(ApexClientCodegen.java:227)
	at org.openapitools.codegen.DefaultCodegen.fromParameter(DefaultCodegen.java:2756)
	at org.openapitools.codegen.DefaultCodegen.fromOperation(DefaultCodegen.java:2425)
	at org.openapitools.codegen.languages.AbstractApexCodegen.fromOperation(AbstractApexCodegen.java:570)
	at org.openapitools.codegen.DefaultGenerator.processOperation(DefaultGenerator.java:964)
	... 5 more

cc @muenzpraeger