Fix flatpak build

The host dconf instance is used in flatpaks.

virt-manager.spec

@@ -32,6 +32,7 @@ Requires: spice-gtk3
 # We can work with gtksourceview 3 or gtksourceview4, pick the latest one
 Requires: gtksourceview4
 
+%if ! 0%{?flatpak}
 # virt-manager is one of those apps that people will often install onto
 # a headless machine for use over SSH. This means the virt-manager dep
 # chain needs to provide everything we need to get a usable app experience.
@@ -39,6 +40,7 @@ Requires: gtksourceview4
 # of usable gsettings backend, so we explicitly depend on dconf so that
 # user settings actually persist across app runs.
 Requires: dconf
+%endif
 
 # The vte291 package is actually the latest vte with API version 2.91, while
 # the vte3 package is effectively a compat package with API version 2.90.
@@ -116,6 +118,7 @@ machine).
 %endif
 
 ./setup.py configure \
+    --prefix=%{_prefix} \
     %{?_default_hvs} \
     %{?_default_graphics}
 
@@ -123,7 +126,7 @@ machine).
 %install
 ./setup.py \
     --no-update-icon-cache --no-compile-schemas \
-    install -O1 --root=%{buildroot}
+    install -O1 --root=%{buildroot} --prefix=%{_prefix}
 %find_lang %{name}
 
 %if 0%{?py_byte_compile:1}