Adds boot 2.4 support in SpringBootVersionVerifier.

The reason errors weren't reported before with boot 2.4 and cloud 2020.0 is because of an error in logic. See gh-895

See also gh-896

spring-cloud-commons/src/main/java/org/springframework/cloud/configuration/SpringBootVersionVerifier.java

@@ -41,6 +41,7 @@ class SpringBootVersionVerifier implements CompatibilityVerifier {
 			this.put("2.1", is2_1());
 			this.put("2.2", is2_2());
 			this.put("2.3", is2_3());
+			this.put("2.4", is2_4());
 		}
 	};
 
@@ -189,6 +190,29 @@ class SpringBootVersionVerifier implements CompatibilityVerifier {
 		};
 	}
 
+	CompatibilityPredicate is2_4() {
+		return new CompatibilityPredicate() {
+
+			@Override
+			public String toString() {
+				return "Predicate for Boot 2.4";
+			}
+
+			@Override
+			public boolean isCompatible() {
+				try {
+					// since 2.4
+					Class.forName("org.springframework.boot.Bootstrapper");
+					return true;
+				}
+				catch (ClassNotFoundException e) {
+					return false;
+				}
+
+			}
+		};
+	}
+
 	private String errorDescription() {
 		String versionFromManifest = getVersionFromManifest();
 		if (StringUtils.hasText(versionFromManifest)) {

spring-cloud-commons/src/test/java/org/springframework/cloud/configuration/SpringBootDependencyTests.java

@@ -21,7 +21,6 @@ import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.atomic.AtomicBoolean;
 
-import org.junit.Ignore;
 import org.junit.Test;
 
 import static org.assertj.core.api.BDDAssertions.then;
@@ -109,12 +108,7 @@ public class SpringBootDependencyTests {
 			}
 		};
 		versionVerifier.ACCEPTED_VERSIONS.clear();
-		versionVerifier.ACCEPTED_VERSIONS.put("2.5", new CompatibilityPredicate() {
-			@Override
-			public boolean isCompatible() {
-				return true;
-			}
-		});
+		versionVerifier.ACCEPTED_VERSIONS.put("2.5", () -> true);
 
 		VerificationResult verificationResult = versionVerifier.verify();
 
@@ -183,11 +177,11 @@ public class SpringBootDependencyTests {
 		then(verificationResult.action).isEmpty();
 	}
 
-	@Ignore // FIXME: https://github.com/spring-cloud/spring-cloud-commons/issues/717
+	//@Ignore // FIXME: https://github.com/spring-cloud/spring-cloud-commons/issues/717
 	@Test
 	public void should_match_against_current_manifest() {
-		verifyCurrentVersionFromManifest("2.3");
-		verifyCurrentVersionFromManifest("2.3.x");
+		verifyCurrentVersionFromManifest("2.4");
+		verifyCurrentVersionFromManifest("2.4.x");
 	}
 
 	private void verifyCurrentVersionFromManifest(String version) {