docs: add sha256 checksums for 12.0.4

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
(cherry picked from commit 7b9d7257b27c15547ffab8d73d10d8a850af364a)
diff --git a/docs/relnotes/12.0.4.html b/docs/relnotes/12.0.4.html
index 78cc4a6..eaa9ba5 100644
--- a/docs/relnotes/12.0.4.html
+++ b/docs/relnotes/12.0.4.html
@@ -31,7 +31,8 @@
 
 <h2>SHA256 checksums</h2>
 <pre>
-TBD
+22026ce4f1c6a7908b0d10ff057decec0a5633afe7f38a0cef5c08d0689f02a6 mesa-12.0.4.tar.gz
+5d6003da867d3f54e5000b4acdfc37e6cce5b6a4459274fdad73e24bd2f0065e mesa-12.0.4.tar.xz
 </pre>