fix(repo): cleanup old plugins promise (#29295)

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## Current Behavior
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When plugins in `nx.json` are changed, the daemon can no longer
communicate with plugin workers and create the graph. It will just hang
waiting for messages to go through.

## Expected Behavior
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-->

Proper cleanup is done when plugins in `nx.json` are changed and the
daemon continues responding properly with project graphs.

## Related Issue(s)
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merged. -->

Fixes #

packages/nx/src/project-graph/plugins/get-plugins.ts

@@ -24,6 +24,7 @@ export async function getPlugins() {
 
   // Cleanup current plugins before loading new ones
   if (cleanup) {
+    pendingPluginsPromise = undefined;
     cleanup();
   }
 
@@ -50,6 +51,7 @@ export async function getOnlyDefaultPlugins() {
 
   // Cleanup current plugins before loading new ones
   if (cleanupDefaultPlugins) {
+    pendingDefaultPluginPromise = undefined;
     cleanupDefaultPlugins();
   }