Run Gitea workflows on Ubuntu only

.gitea/workflows/skia.yml

@@ -21,30 +21,3 @@ jobs:
           cargo test -p libremetaverse-imaging-skia --no-default-features
           cargo test -p libremetaverse-imaging-skia --features skia
           cargo package -p libremetaverse-imaging-skia --list
-
-  macos:
-    runs-on: macos-latest
-    env:
-      FORCE_SKIA_BINARIES_DOWNLOAD: "1"
-    steps:
-      - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@stable
-      - name: Test default and Skia feature builds
-        run: |
-          cargo test -p libremetaverse-imaging-skia --no-default-features
-          cargo test -p libremetaverse-imaging-skia --features skia
-          cargo package -p libremetaverse-imaging-skia --list
-
-  windows:
-    runs-on: windows-latest
-    env:
-      FORCE_SKIA_BINARIES_DOWNLOAD: "1"
-    steps:
-      - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@stable
-      - name: Test default and Skia feature builds
-        shell: pwsh
-        run: |
-          cargo test -p libremetaverse-imaging-skia --no-default-features
-          cargo test -p libremetaverse-imaging-skia --features skia
-          cargo package -p libremetaverse-imaging-skia --list