fix(runner): bring concurrency back

Author: folke

lua/lazy/manage/runner.lua

@@ -96,19 +96,21 @@ function Runner:_start()
         waiting = waiting + 1
         wait_step = s.step
       elseif not running then
-        local plugin = self:plugin(name)
-        if s.step == #self._pipeline then
-          s.task = nil
-          plugin._.working = false
-        elseif s.step < #self._pipeline then
-          active = active + 1
-          s.step = s.step + 1
-          step = self._pipeline[s.step]
-          if step.task == "wait" then
+        if not self._opts.concurrency or active < self._opts.concurrency then
+          local plugin = self:plugin(name)
+          if s.step == #self._pipeline then
+            s.task = nil
             plugin._.working = false
-          else
-            s.task = self:queue(plugin, step)
-            plugin._.working = not not s.task
+          elseif s.step < #self._pipeline then
+            active = active + 1
+            s.step = s.step + 1
+            step = self._pipeline[s.step]
+            if step.task == "wait" then
+              plugin._.working = false
+            else
+              s.task = self:queue(plugin, step)
+              plugin._.working = not not s.task
+            end
           end
         end
       else