fix(devkit): detect package manager based on install location (#27127)

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## Current Behavior
<!-- This is the behavior we have today -->

The package manager is detected based off of the relative `cwd` which in
most cases is `''`. This incorrectly goes off of the `cwd` of the
command rather than the location of the `package.json` file being
modified.

## Expected Behavior
<!-- This is the behavior we should expect with the changes in this PR
-->

The package manager is detected based off the absolute path of the
directory containing the `package.json` file being modified. So if this
is the root, it will detect the package manager at the root rather than
the `cwd`

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

Fixes https://github.com/nrwl/nx/issues/19831

packages/devkit/src/tasks/install-packages-task.ts

@@ -20,7 +20,7 @@ export function installPackagesTask(
   tree: Tree,
   alwaysRun: boolean = false,
   cwd: string = '',
-  packageManager: PackageManager = detectPackageManager(cwd)
+  packageManager: PackageManager = detectPackageManager(join(tree.root, cwd))
 ): void {
   if (
     !tree