manuals: fix epub export warnings

Needed now that warnings are turned into errors

(From yocto-docs rev: 3f99cff8c6c672967eb09f6950d16ed30260ca68)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/conf.py

@@ -92,6 +92,9 @@ intersphinx_mapping = {
     'bitbake': ('https://docs.yoctoproject.org/bitbake/', None)
 }
 
+# Suppress "WARNING: unknown mimetype for ..."
+suppress_warnings = ['epub.unknown_project_files']
+
 # -- Options for HTML output -------------------------------------------------
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for