Do not use query components in URLs for assets in EPUB rendering

If the EPUB builder is detected, do not add checksums in a query
component to the URL of css and js assets.

The XHTML in EPUBs does not allow the use of query components in
relative URLs.
The checksumming of assets, introduced in
ae20669 unconditionally adds a query
component for the checksum, which breaks rendering on many enduser
devices (tested on e.g. Kindle Paperwhite 3, Kobo Aura H2O Edition 2).

Fixes sphinx-doc#11598

Signed-off-by: David Runge <dave@sleepmap.de>

CHANGES.rst

@@ -47,6 +47,8 @@ Bugs fixed
   package (triggered if using ``fontenc`` with ``T2A`` option and document
   language is not a Cyrillic one).
   Patch by Jean-François B.
+* #11598: Do not use query components in URLs for assets in EPUB rendering.
+  Patch by David Runge.
 
 Testing
 -------

sphinx/builders/html/__init__.py

@@ -1061,7 +1061,9 @@ def css_tag(css: _CascadingStyleSheet) -> str:
                     attrs.append(f'{key}="{html.escape(value, quote=True)}"')
             uri = pathto(os.fspath(css.filename), resource=True)
             if checksum := _file_checksum(outdir, css.filename):
-                uri += f'?v={checksum}'
+                # the EPUB format does not allow the use of query components
+                if self.name != 'epub':
+                    uri += f'?v={checksum}'
             return f'<link {" ".join(sorted(attrs))} href="{uri}" />'
 
         ctx['css_tag'] = css_tag
@@ -1092,7 +1094,9 @@ def js_tag(js: _JavaScript | str) -> str:
                 # https://github.com/sphinx-doc/sphinx/issues/11658
                 pass
             elif checksum := _file_checksum(outdir, js.filename):
-                uri += f'?v={checksum}'
+                # the EPUB format does not allow the use of query components
+                if self.name != 'epub':
+                    uri += f'?v={checksum}'
             if attrs:
                 return f'<script {" ".join(sorted(attrs))} src="{uri}"></script>'
             return f'<script src="{uri}"></script>'