CI: Don't build the material gallery for every CI build

It's just built in the nightly. On macOS in the CI it's built twice, once as bin and once as lib, with a total of 600seconds according to cargo-timings.

Author: tronical

.github/workflows/ci.yaml

@@ -75,7 +75,7 @@ jobs:
             os: ${{ matrix.os }}
             name: ${{ matrix.name }}
             rust_version: ${{ matrix.rust_version }}
-            extra_args: ${{ matrix.extra_args }}
+            extra_args: ${{ matrix.extra_args }} --exclude material-gallery
             save_if: ${{ matrix.save_if }}
             timeout_minutes: 120