test: properly gate a zstd section
This part of the test can't run if zstd is not available. This was caught by
--pure test (who don't support zstd).
--- a/tests/test-repo-compengines.t Mon May 20 07:11:06 2019 +0200
+++ b/tests/test-repo-compengines.t Mon May 20 07:11:16 2019 +0200
@@ -139,6 +139,8 @@
abort: invalid value for `storage.revlog.zlib.level` config: 42
[255]
+#if zstd
+
checking zstd options
=====================
@@ -194,3 +196,4 @@
abort: invalid value for `storage.revlog.zstd.level` config: 42
[255]
+#endif