[gtk-doc] Reapply and fix previous change.

[Stefan Sauer <stefkost src gnome org>]

commit 12d9a698fb58f3d1a840d3bfc0d15a3a9f57afc1
Author: Stefan Sauer <ensonic users sf net>
Date:   Mon May 27 16:37:07 2019 +0200

    Reapply and fix previous change.
    
    This is required for make dist-check and some distro-packages. But now
    pick sensible permissions.
    
    Revert "Revert "highlight: make style-file writable before appending""
    
    This reverts commit 9467f121fb728866a2366df65805aea1a587ac7e.
    
    See #84

 gtkdoc/highlight.py | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gtkdoc/highlight.py b/gtkdoc/highlight.py
index 6023d33..ba1c601 100644
--- a/gtkdoc/highlight.py
+++ b/gtkdoc/highlight.py
@@ -22,6 +22,7 @@
 """
 Highlight sourcecode snippets.
 """
+import os
 
 from pygments import highlight
 from pygments.lexers import CLexer
@@ -45,5 +46,6 @@ def highlight_code(code, lang='c'):
 
 
 def append_style_defs(css_file_name):
+    os.chmod(css_file_name, 0o644)
     with open(css_file_name, 'at', newline='\n', encoding='utf-8') as css:
         css.write(HTML_FORMATTER.get_style_defs())