community/optipng: security upgrade to 0.7.8

The changelog does not mention the CVE, but i think it is actually solved in this version, not 0.7.7. If i turn out to be wrong, then the secfixes section can be amended again.

community/optipng/APKBUILD

@@ -11,7 +11,7 @@ subpackages="$pkgname-doc"
 source="https://downloads.sourceforge.net/sourceforge/optipng/optipng-$pkgver.tar.gz"
 
 # secfixes:
-#   0.7.7-r0:
+#   0.7.8-r0:
 #     - CVE-2023-43907
 
 build() {