Reduce grain counts in ManualCollectionShouldNotCollectBusyActivations to 20 each

CI environments have more limited thread pool capacity than local machines.
Even 100 blocked grains exhausts the thread pool, causing ForceActivationCollection
to timeout. Reducing to 20 grains is sufficient to test the functionality while
avoiding thread pool starvation.

Author: ReubenBond

.gitignore

@@ -220,3 +220,4 @@ src/SetupTestScriptOutput.txt
 
 # code coverage
 *.cobertura.xml
+OrleansTestSecrets.json

test/TesterInternal/ActivationsLifeCycleTests/ActivationCollectorTests.cs

@@ -274,14 +274,15 @@ public async Task ManualCollectionShouldNotCollectBusyActivations()
             // 2. Busy activations remain not-inactive (IsCurrentlyExecuting = true) regardless of time
             // 3. The collector only collects activations that are both inactive AND stale
             //
-            // NOTE: We use smaller grain counts (100 each) compared to the automatic collection test (500 each)
+            // NOTE: We use much smaller grain counts (20 each) compared to the automatic collection test (500 each)
             // because we need to call ForceActivationCollection while grains are blocked. Blocking too many grains
             // exhausts the silo thread pool and causes the management grain call to timeout.
+            // CI environments have limited thread pool capacity, so we keep the count very low.
             await Initialize(DEFAULT_IDLE_TIMEOUT, useFakeTimeProvider: true);
 
             TimeSpan shortIdleTimeout = TimeSpan.FromSeconds(1);
-            const int idleGrainCount = 100;
-            const int busyGrainCount = 100;
+            const int idleGrainCount = 20;
+            const int busyGrainCount = 20;
             var idleGrainTypeName = RuntimeTypeNameFormatter.Format(typeof(IdleActivationGcTestGrain1));
             var busyGrainTypeName = RuntimeTypeNameFormatter.Format(typeof(BusyActivationGcTestGrain1));