Previously, if spring.main.web-application-type was configured in
application.properties to servlet or reactive, setting
webEnvironment=NONE on @SpringBootTest would not work correctly and
a servlet or reactive web application context would be created
based on the value of spring.main.web-application-type.
This commit updates the test context bootstapper to set
spring.main.web-application-type to none when webEnvironment has been
set to none. This is done in the merged context configuration's
property source properties which are applied to the environment in a
high-precedence test property source that will override configuration
in application.properties.
Closes gh-29695
