temp/megapixels-purism: bump pkgrel (MR 3771)

Fix for:
  missing depend(s): so:libcamera.so.0.0.2

[ci:skip-build]: already built successfully in CI

temp/megapixels-purism/APKBUILD

 # Purism's fork of megapixels, for the Librem 5
 pkgname=megapixels-purism
 pkgver=0.19.0
-pkgrel=5
+pkgrel=6
 pkgdesc="GTK+3 camera app for mobile devices"
 url="https://source.puri.sm/Librem5/millipixels"
 arch="all"