Assert Error-Messages already includes dashes

When the cert-content is not valid, the assert output message is not correct.
Because it outputs too many dashes .The const X509- and PKCS8-PEM_HEADER already includes the dashes.

I took the output message via copy and paste, but it was still not valid ;-(

Only the output is affected, the checks itself is correct.

core/src/main/java/org/springframework/security/converter/RsaKeyConverters.java

@@ -83,8 +83,8 @@ public final class RsaKeyConverters {
 		return (source) -> {
 			List<String> lines = readAllLines(source);
 			Assert.isTrue(!lines.isEmpty() && lines.get(0).startsWith(PKCS8_PEM_HEADER),
-					"Key is not in PEM-encoded PKCS#8 format, please check that the header begins with -----"
-							+ PKCS8_PEM_HEADER + "-----");
+					"Key is not in PEM-encoded PKCS#8 format, please check that the header begins with "
+							+ PKCS8_PEM_HEADER);
 			StringBuilder base64Encoded = new StringBuilder();
 			for (String line : lines) {
 				if (RsaKeyConverters.isNotPkcs8Wrapper(line)) {