v3.120.3

This minor release fixes a number of regressions surrounding memory
imports and DRM modifiers, specifically aimed at issues that arose with
mpv's --hwdec=vaapi.

Changes:
- `pl_fmt.modifiers` now always includes DRM_FORMAT_MOD_INVALID on
   OpenGL, which instructs the implementation to not specify modifiers
- passing a DRM modifier not in the list of supported modifiers is now
  considered a hard error, to rule out non-working hwaccel formats

Fixes:
- fix a crash when using sampling shaders on textures with unknown formats
- fix improperly specified SDL header imports in the demos
- fix an issue where the vulkan texture handle capabilities were testing
  for presence of the wrong extension
- fix an issue where non-enabled DRM modifier structs were accidentally
  linked into the pNext chain, causing issues with some drivers
This tag has no release notes.