Update documentation to reflect that we test under more environments:

- [Windows](#2686)
- [Java 17](#5801)

index.md

@@ -113,10 +113,11 @@ flavor.
 5.  Our classes are not designed to protect against a malicious caller. You
     should not use them for communication between trusted and untrusted code.
 
-6.  For the mainline flavor, we test the libraries using only OpenJDK 8 and
-    OpenJDK 11 on Linux. Some features, especially in `com.google.common.io`,
-    may not work correctly in other environments. For the Android flavor, our
-    unit tests also run on API level 15 (Ice Cream Sandwich).
+6.  For the mainline flavor, we test the libraries using OpenJDK 8, 11, and 17
+    on Linux, with some additional testing on newer JDKs and on Windows. Some
+    features, especially in `com.google.common.io`, may not work correctly in
+    non-Linux environments. For the Android flavor, our unit tests also run on
+    API level 15 (Ice Cream Sandwich).
 
 [guava-snapshot-api-docs]: https://guava.dev/releases/snapshot-jre/api/docs/
 [guava-snapshot-api-diffs]: https://guava.dev/releases/snapshot-jre/api/diffs/