Skip region validation in S3BlobStoreRepositoryTests (elastic#127372)

Today these tests assert that the requests received by the handler are
signed in region `us-east-1` with no region specified, but in fact when
running in EC2 the SDK will pick up the actual region which may be
different. This commit skips this region validation for now (it is
tested elsewhere).

(cherry picked from commit 15b6e85)

Author: DaveCTurner

modules/repository-s3/src/internalClusterTest/java/org/elasticsearch/repositories/s3/S3BlobStoreRepositoryTests.java

@@ -617,7 +617,9 @@ public void handle(final HttpExchange exchange) throws IOException {
             assertTrue(
                 isValidAwsV4SignedAuthorizationHeader(
                     "test_access_key",
-                    Objects.requireNonNullElse(region, "us-east-1"),
+                    // If unset, the region used by the SDK is usually going to be `us-east-1` but sometimes these tests run on bare EC2
+                    // machines and the SDK picks up the region from the IMDS there, so for now we use '*' to skip validation.
+                    Objects.requireNonNullElse(region, "*"),
                     "s3",
                     exchange.getRequestHeaders().getFirst("Authorization")
                 )