CI: Disable Windows, MacOS Testing

Windows CI runners appear to be very slow wrt. the time limits we've set for many of the tests, so fail for tests involving longer files. At the same time, MacOS tests aren't likely to add much value over Linux.

This commit disables *test* runners for these environments to remove a lot of commit/PR noise. Builds are still run on these platforms.

.github/workflows/ci.yml

@@ -48,8 +48,10 @@ jobs:
             toolchain: nightly
           - name: macOS
             os: macOS-latest
+            dont-test: true
           - name: Windows
             os: windows-latest
+            dont-test: true
           - name: driver only
             features: driver rustls
             dont-test: true
@@ -108,7 +110,7 @@ jobs:
         run: cargo build --features full-doc
 
       - name: Test all features
-        if: matrix.features == ''
+        if: ${{ !matrix.dont-test && matrix.features == '' }}
         run: cargo test --features full-doc
 
       - name: Build some features