Improve stability of FixedSizeCacheTest identity/weak tests (#9362)

by eliminating the chance identity hash might collide even after 3 rehashes
the easiest way to do this is to bump the size of the cache used in testing

note this is only necessary because we want to keep both keys in the cache
to test the 'visit' method - otherwise we'd need to relax that assertion

Author: mcculls

internal-api/src/test/groovy/datadog/trace/api/cache/FixedSizeCacheTest.groovy

@@ -112,7 +112,7 @@ class FixedSizeCacheTest extends DDSpecification {
 
   def "identity cache should store and retrieve values"() {
     setup:
-    def fsCache = DDCaches.newFixedSizeIdentityCache(15)
+    def fsCache = DDCaches.newFixedSizeIdentityCache(256)
     def creationCount = new AtomicInteger(0)
     def tvc = new TVC(creationCount)
     fsCache.computeIfAbsent(id1, tvc)
@@ -140,7 +140,7 @@ class FixedSizeCacheTest extends DDSpecification {
 
   def "weak key cache should store and retrieve values"() {
     setup:
-    def fsCache = DDCaches.newFixedSizeWeakKeyCache(15)
+    def fsCache = DDCaches.newFixedSizeWeakKeyCache(256)
     def creationCount = new AtomicInteger(0)
     def tvc = new TVC(creationCount)
     fsCache.computeIfAbsent(id1, tvc)