distgit: disable mod_deflate for lookaside cache in staging

Fixes #12812.

This disables mod_deflate for the lookaside cache directory to prevent
incorrect 'Content-Encoding: gzip' headers being sent with archives.
Wrapped in a staging block for initial testing as requested.

Signed-off-by: Victor Koycheff <victorkoycheff@gmail.com>

roles/distgit/templates/lookaside.conf

@@ -3,5 +3,12 @@ Alias /lookaside        /srv/cache/lookaside
     Options Indexes FollowSymLinks
     AllowOverride None
     Require all granted
+    
+{% if env == 'staging' %}
+    # Disable global mod_deflate for lookaside cache 
+    # to prevent double-compression and false gzip headers
+    SetEnv no-gzip 1
+    SetEnv dont-vary 1
+{% endif %}
 </Directory>