2.4 -> 2.5: Prefer using AssertJ assertThat(...)

[BoykoAlex]

org.springframework.boot.test.context.assertj.ApplicationContextAssertProvider.assertThat()

to prevent accidental use. Prefer standard AssertJ assertThat(context)... calls instead.

org.springframework.boot.test.json.JsonContent.assertThat()

to prevent accidental use. Prefer standard AssertJ assertThat(context)... calls instead.

This is not an obvious search/replace unfortunately. Might be the case for manual migration rather than automatic.