ci: Unbreak Mac CI by adding jpeg-xl install (AcademySoftwareFoundation#5139)

It must have been among the homebrew packages in the base Mac
installation on GHA, until just a couple days ago?

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/build-scripts/install_homebrew_deps.bash

@@ -35,6 +35,7 @@ if [[ "$OIIO_BREW_INSTALL_PACKAGES" == "" ]] ; then
         expat \
         ffmpeg \
         imath \
+        jpeg-xl \
         libheif \
         libraw \
         libultrahdr \