Mosaic fails with a mix of GrayAlpha and RGBA images

Description

The actual issue is down in JAI-EXT, which provides the support for mixed color model mosaics.
This also affects a GeoPackage test, in which a mix of RGB and RGBA images are composed, and the output is currently RGB instead of RGBA.

JAI-EXT issue here: https://github.com/geosolutions-it/jai-ext/issues/206

Environment

None

Assignee

Andrea Aime

Reporter

Andrea Aime

Triage

None

Components

Fix versions

Priority

Medium
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