meson: bump test-timeout

This tests usually takes around 15 seconds on CI, according to logs. It
recently timed out under load, causing a job to fail spuriously.

Let's bump the timeout here to 60. That's in line with the glsl compiler
warnings test, which usually takes around the same time.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29547>

src/compiler/glsl/tests/meson.build

@@ -119,6 +119,7 @@ if with_tools.contains('glsl')
               glsl_compiler
             ],
       suite : ['compiler', 'glsl'],
+      timeout: 60,
     )
   endif
 endif