sstate: Fixes for eSDK generation after zstd switch

(From OE-Core rev: f5a90df08631117cd66bec68cb1851db96822bb8)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/gen-lockedsig-cache

@@ -94,8 +94,7 @@ print("Gathering file list took %.1fs" % elapsed)
 print('Processing files')
 for f in files:
     sys.stdout.write('Processing %s... ' % f)
-    _, ext = os.path.splitext(f)
-    if not ext in ['.tgz', '.siginfo', '.sig']:
+    if not f.endswith(('.tar.zst', '.siginfo', '.sig')):
         # Most likely a temp file, skip it
         print('skipping')
         continue