Fix effect updating its own source looping in strict mode

src/graph.luau

@@ -175,7 +175,7 @@ local update_queue = { n = 0 } :: { n: number, [number]: Node<any> }
 local function try_evaluate_node<T>(node: Node<T>): (boolean, string?)
     if flags.strict then
         if table.find(scopes, node) then
-            error("a scope, that should rerun due to the update of a source, is already active", 0)
+            return false, "a scope, that should rerun due to the update of a source, is already active"
         end
 
         local initial_value = node.cache

test/tests.luau

@@ -3171,6 +3171,21 @@ TEST("strict", wrap_root(function()
         CHECK(count == 4)
     end
 
+    do CASE "effect updating its own source"
+        local src = source(0)
+        local count = 0
+
+        effect(function()
+            count += 1
+            if count > 100 then return end
+            local v = src()
+            if v > 0 then src(v + 1) end
+        end)
+
+        CHECK(not pcall(src, 1))
+        CHECK(count < 100)
+    end
+
     do CASE "destruction of active scope"
         local src = source(false)
         local count = 0