Update release notes

Author: DennisHeimbigner

RELEASE_NOTES.md

@@ -7,7 +7,7 @@ This file contains a high-level description of this package's evolution. Release
 
 ## 4.9.3 - TBD
 
-* Fix default parameters for caching of NCZarr. See [Github #????](https://github.com/Unidata/netcdf-c/pull/????).
+* Fix default parameters for caching of NCZarr. See [Github #2734](https://github.com/Unidata/netcdf-c/pull/2734).
 * Introducing configure-time options to disable various filters, even if the required libraries are available on the system, in support of [GitHub #2712](https://github.com/Unidata/netcdf-c/pull/2712). 
 * Fix memory leak WRT unreclaimed HDF5 plist. See [Github #2752](https://github.com/Unidata/netcdf-c/pull/2752).
 * Support HDF5 transient types when reading an HDF5 file.  See [Github #2724](https://github.com/Unidata/netcdf-c/pull/2724).