Only run the gzip test on Linux CI

This test fails when a MIME database isn't present, such as the
Windows CI environment or minimal environments (reported in #478).

.github/workflows/test.yml

@@ -9,7 +9,10 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@1.57.0
-      - run: cargo test
+      # This also runs tests that rely on the MIME database being
+      # present.
+      - name: Run all tests, including ignored tests
+        run: cargo test -- --ignored
 
   test_linux_latest_stable:
     name: Test Linux (latest stable Rust)

src/files.rs

@@ -289,6 +289,7 @@ mod tests {
     }
 
     #[test]
+    #[ignore]
     fn test_gzip_is_binary() {
         // Bytes for "echo "[]" | gzip -c | hexdump -C"
         let bytes = vec![