Guard against missing file in CI upload (elastic#117889)

Somehow files can be lost before the build ends up uploading them,
presumable from temporarily file deletion after tests complete. This
commit guards against this case so that the build will not completely
fail, but instead log a warning.

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/ElasticsearchBuildCompletePlugin.java

@@ -29,6 +29,8 @@
 import org.gradle.api.provider.Property;
 import org.gradle.api.tasks.Input;
 import org.jetbrains.annotations.NotNull;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.io.BufferedInputStream;
 import java.io.BufferedOutputStream;
@@ -47,6 +49,8 @@
 
 public abstract class ElasticsearchBuildCompletePlugin implements Plugin<Project> {
 
+    private static final Logger log = LoggerFactory.getLogger(ElasticsearchBuildCompletePlugin.class);
+
     @Inject
     protected abstract FlowScope getFlowScope();
 
@@ -241,8 +245,11 @@ private static void createBuildArchiveTar(List<File> files, File projectDir, Fil
                 tOut.setLongFileMode(TarArchiveOutputStream.LONGFILE_GNU);
                 tOut.setBigNumberMode(TarArchiveOutputStream.BIGNUMBER_STAR);
                 for (Path path : files.stream().map(File::toPath).toList()) {
-                    if (!Files.isRegularFile(path)) {
-                        throw new IOException("Support only file!");
+                    if (Files.exists(path) == false) {
+                        log.warn("File disappeared before it could be added to CI archive: " + path);
+                        continue;
+                    } else if (!Files.isRegularFile(path)) {
+                        throw new IOException("Support only file!: " + path);
                     }
 
                     long entrySize = Files.size(path);