docs: add sha256 checksums for 11.0.8

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
(cherry picked from commit b9b19162ee)

docs/relnotes/11.0.8.html

@@ -31,7 +31,8 @@ because compatibility contexts are not supported.
 
 <h2>SHA256 checksums</h2>
 <pre>
-TBD
+ab9db87b54d7525e4b611b82577ea9a9eae55927558df57b190059d5ecd9406f  mesa-11.0.8.tar.gz
+5696e4730518b6805d2ed5def393c4293f425a2c2c01bd5ed4bdd7ad62f7ad75  mesa-11.0.8.tar.xz
 </pre>