Explicit error message if source is not an archive

This commit split the existing assertion to provide an explicit error
message if the source file is not an archive.

See gh-31997

spring-boot-project/spring-boot-tools/spring-boot-jarmode-layertools/src/main/java/org/springframework/boot/jarmode/layertools/Context.java

@@ -55,7 +55,8 @@ class Context {
 	 * @param workingDir the working directory
 	 */
 	Context(File archiveFile, File workingDir) {
-		Assert.state(isExistingFile(archiveFile) && isJarOrWar(archiveFile), "Unable to find source archive");
+		Assert.state(isExistingFile(archiveFile), "Unable to find source archive");
+		Assert.state(isJarOrWar(archiveFile), "Source archive doesn't end with .jar or .war");
 		this.archiveFile = archiveFile;
 		this.workingDir = workingDir;
 		this.relativeDir = deduceRelativeDir(archiveFile.getParentFile(), this.workingDir);