Reinstate SNAPSHOT updates in integration tests

[bclozel]

In fa4a3ab, we removed forced SNAPSHOT updates as an attempt to solve #12689.

In recent builds, and after incompatible changes made in Framework and Boot for #16427, we got several failed builds like:

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APPLICATION FAILED TO START
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Description:

An attempt was made to call a method that does not exist. The attempt was made from the following location:

    org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration$EnableWebMvcConfiguration.requestMappingHandlerAdapter(WebMvcAutoConfiguration.java:494)

The following method did not exist:

    org.springframework.web.servlet.config.annotation.DelegatingWebMvcConfiguration.requestMappingHandlerAdapter(Lorg/springframework/web/accept/ContentNegotiationManager;Lorg/springframework/format/support/FormattingConversionService;Lorg/springframework/validation/Validator;)Lorg/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerAdapter;

The method's class, org.springframework.web.servlet.config.annotation.DelegatingWebMvcConfiguration, is available from the following locations:

    jar:file:/tmp/build/14ea0570/git-repo/spring-boot-tests/spring-boot-integration-tests/spring-boot-devtools-tests/target/dependencies/spring-webmvc-5.2.0.BUILD-SNAPSHOT.jar!/org/springframework/web/servlet/config/annotation/DelegatingWebMvcConfiguration.class

It was loaded from the following location:

    file:/tmp/build/14ea0570/git-repo/spring-boot-tests/spring-boot-integration-tests/spring-boot-devtools-tests/target/dependencies/spring-webmvc-5.2.0.BUILD-SNAPSHOT.jar

This points to an incompatible method signature between Framework and Boot, but this is not consistent with the previous steps of the build since other modules were OK. This pointed to a stale SNAPSHOT in the build-integration-tests task.

This issue is about reinstating the SNAPSHOT updates in that task to avoid future issues like this.