Fix Zipkin receiver wrong condition for decoding `gzip` (#8592)

CHANGES.md

@@ -63,6 +63,7 @@ Release Notes.
 * Set default connection timeout of ElasticSearch to 3000 milliseconds.
 * Support ElasticSearch 8 and add it into E2E tests.
 * Disable indexing for field `alarm_record.tags_raw_data` of binary type in ElasticSearch storage.
+* Fix Zipkin receiver wrong condition for decoding `gzip`. 
 
 #### UI
 

oap-server/server-receiver-plugin/zipkin-receiver-plugin/src/main/java/org/apache/skywalking/oap/server/receiver/zipkin/handler/SpanProcessor.java

@@ -58,7 +58,7 @@ public class SpanProcessor {
     private InputStream getInputStream(HttpServletRequest request) throws IOException {
         InputStream requestInStream;
 
-        String headEncoding = request.getHeader("accept-encoding");
+        String headEncoding = request.getHeader("Content-Encoding");
         if (headEncoding != null && (headEncoding.indexOf("gzip") != -1)) {
             requestInStream = new GZIPInputStream(request.getInputStream());
         } else {