Consistently log exceptions from TestExecutionListeners at WARN level

Prior to this commit, the TestContextManager logged an exception from a
TestExecutionListener at WARN level except in prepareTestInstance()
where such an exception was logged at ERROR level (except for a skipped
exception which is logged at INFO level).

For consistency, this commit modifies TestContextManager so that it
always logs non-skipped exceptions from TestExecutionListeners at WARN
level.

Closes gh-31688

spring-test/src/main/java/org/springframework/test/context/TestContextManager.java

@@ -268,8 +268,8 @@ public class TestContextManager {
 										.formatted(typeName(testExecutionListener), testInstance), ex);
 						}
 					}
-					else if (logger.isErrorEnabled()) {
-						logger.error("""
+					else if (logger.isWarnEnabled()) {
+						logger.warn("""
 							Caught exception while allowing TestExecutionListener [%s] to \
 							prepare test instance [%s]"""
 								.formatted(typeName(testExecutionListener), testInstance), ex);