Refactor assertions to use `assertThat` with appropriate matchers #6841

Job	Run time
build	6m 0s
checkstyle	3m 58s
shellcheck	3m 9s
copyright	3m 25s
spotbugs/core	10m 29s
tests/core	10m 54s
tests/tck-cdi	17m 24s
spotbugs/integrations	7m 14s
tests/it	13m 6s
tests/native-image-mp-1-linux	6m 41s
tests/tck-rest	14m 33s
spotbugs/others	12m 34s
tests/dbclient	8m 4s
tests/native-image-mp-2-linux	13m 12s
tests/tck-others	16m 48s
tests/native-image-mp-3-linux	6m 29s
tests/dbclient-oracle	16m 42s
tests/native-image-se-1-linux	6m 43s
archetypes/r1-jar	6m 49s
tests/others	12m 28s
docs	4m 36s
tests/native-image-inject-linux	6m 46s
archetypes/r2-jar	6m 41s
tests/native-image-mp-1-macos	9m 15s
examples/linux	9m 53s
javadoc (core)	6m 43s
tests/native-image-mp-2-macos	14m 49s
archetypes/r3-jar	5m 54s
examples/macos	9m 10s
javadoc (integrations)	5m 14s
tests/native-image-mp-3-macos	8m 37s
archetypes/r4-jar	6m 48s
javadoc (others)	7m 42s
tests/native-image-se-1-macos	8m 37s
archetypes/r5-jar	5m 6s
archetypes/legacy	4m 44s
tests/native-image-inject-macos	6m 8s
tests/packaging-jar-linux	6m 59s
quickstarts/linux	11m 45s
tests/packaging-jlink-linux	8m 38s
quickstarts/macos	14m 14s
tests/packaging-jar-macos	5m 40s
tests/packaging-jlink-macos	6m 39s
tests/results	12s
gate	3s
	6h 17m 35s

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