CI: disable rust nightly jobs

Until https://github.com/rust-lang/rust/issues/129601 is fixed

.github/workflows/build_docs.yaml

@@ -43,7 +43,7 @@ jobs:
             - uses: ./.github/actions/install-linux-dependencies
             - uses: ./.github/actions/setup-rust
               with:
-                  toolchain: nightly
+                  toolchain: nightly-2024-08-20 # pinned because of https://github.com/rust-lang/rust/issues/129601
                   components: rustfmt
                   target: aarch64-linux-android
             - name: Install mdbook

.github/workflows/ci.yaml

@@ -35,8 +35,9 @@ jobs:
                     - os: windows-2022
                       rust_version: "beta"
                       extra_args: "--exclude ffmpeg --exclude gstreamer-player"
-                    - os: ubuntu-22.04
-                      rust_version: "nightly"
+                    # disabled until https://github.com/rust-lang/rust/issues/129601 is fixed
+                    #- os: ubuntu-22.04
+                    #  rust_version: "nightly"
                 exclude:
                     - os: macos-12
                       rust_version: "1.73"