libde265-dev is needed too

.github/workflows/test.yml

@@ -30,7 +30,9 @@ jobs:
         run:
           sudo apt-get update -qq -o Acquire::Retries=3
 
-      # libaom-dev is required by libheif-dev in the ppa, but not listed
+      # libaom-dev and libde265-dev are required by the libheif.pc in 
+      # libheif-dev in the ppa, but not listed as deps in the debian package
+      # see https://github.com/strukturag/libheif/issues/404
       - name: Install platform dependencies
         env:
           DEBIAN_FRONTEND: noninteractive
@@ -48,6 +50,7 @@ jobs:
                 libwebp-dev
                 libtiff5-dev
                 libaom-dev
+                libde265-dev
                 libheif-dev
                 libexpat1-dev
                 libcfitsio-dev