message: Update RELEASE_NOTES for 1.9.24
diff: This file contains one line summaries of commits that are worthy of mentioning in release notes.
  A new header is inserted each time a *tag* is created.
  -## Next release (main branch)
  +## v1.9.26 (currently main branch)
  +
  +## v1.9.25
  - engine: new screen-space lens flare
  -- engine: new experimental tone mapper, `EVILS` (name will most likely change)
  ## v1.9.24
  +- engine: Fix memory leaks in OpenGL driver.
  +- engine: new experimental tone mapper, `EVILS` (name will most likely change).
  +- engine: Improvements to Vulkan backend.
  +- engine: Fix incorrect units documented for `LightManager.getIntensity`.
  +- engine: fix high quality upsampling for SSAO.
  +- engine: implement accurate normal reconstruction for SSAO.
  +- engine: improve LOW and HIGH quality levels for SSAO.
  +- libs: improvements to `libiblprefilter`.
  +- materials: New `quality` property.
  +- samples: Add new gltf-viewer iOS sample.
  +- samples: clear the background in lightbulb sample.
  +
  ## v1.9.23
  - Vulkan: various fixes.
  