Log Message:
openexr: update to 3.1.8.

## Version 3.1.8 (June 2, 2023)

Patch release that addresses miscellaneous build issues, for macOS in
particular, but also includes:

* Support for DWA compression in OpenEXRCore
* Fix for threadpool deadlocks during shutdown on Windows

This release also addresses:

* OSS-fuzz 59070 Stack-buffer-overflow in DwaCompressor_readChannelRules