RepositoryCache: declare schedulerLock final

This fixes errorprone error [SynchronizeOnNonFinalField]: Synchronizing
on non-final fields is not safe: if the field is ever updated, different
threads may end up locking on different objects.

Change-Id: I42fe5bde825151693e2da2d5b6cd6e1d34038dbc
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/RepositoryCache.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/RepositoryCache.java
index c1beb6f..41f291b 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/RepositoryCache.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/RepositoryCache.java
@@ -202,7 +202,7 @@
 
 	private volatile long expireAfter;
 
-	private Object schedulerLock = new Lock();
+	private final Object schedulerLock = new Lock();
 
 	private RepositoryCache() {
 		cacheMap = new ConcurrentHashMap<>();