Add CodeQL suppression for intentional string identity comparison

The lgtm[java/reference-equality-on-strings] comment suppresses CodeQL
for the ABSENT_SENTINEL identity check. Java's @SuppressWarnings is not
honored by CodeQL's analysis engine.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: c4e523e3-9d39-4598-90ec-54d959c44ce8

Author: edburns

java/sdk/src/test/java/com/github/copilot/ffi/InProcessEnvGuard.java

@@ -123,7 +123,7 @@ public void close() {
             // Identity comparison is intentional: ABSENT_SENTINEL is a unique instance
             // used to distinguish "env var was absent" from "env var was empty string".
             @SuppressWarnings("StringEquality")
-            boolean wasAbsent = entry.getValue() == ABSENT_SENTINEL;
+            boolean wasAbsent = entry.getValue() == ABSENT_SENTINEL; // lgtm[java/reference-equality-on-strings]
             String restoreValue = wasAbsent ? null : entry.getValue();
             nativeSetEnv(entry.getKey(), restoreValue);
         }