minor symfony#20772 Update virtual-machine.rst (EtienneHosman)

This PR was submitted for the 7.2 branch but it was merged into the 6.4 branch instead.

Discussion
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Update virtual-machine.rst

Syntax error: made 'all' a string

Commits
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c679fe5 Update virtual-machine.rst

Author: javiereguiluz

frontend/encore/virtual-machine.rst

@@ -107,7 +107,7 @@ the dev-server. To fix this, set the ``allowedHosts`` option:
         // ...
 
         .configureDevServerOptions(options => {
-            options.allowedHosts = all;
+            options.allowedHosts = 'all';
         })
 
 .. warning::