Add NEWS entry for bug #77357

The fix has been confirmed.

[ci skip]

Author: nikic

NEWS

@@ -7,6 +7,8 @@ PHP                                                                        NEWS
     (Laruence)
   . Fixed bug #77376 ("undefined function" message no longer includes
     namespace). (Laruence)
+  . Fixed bug #77357 (base64_encode / base64_decode doest not work on nested
+    VM). (Nikita)
   . Fixed bug #77339 (__callStatic may get incorrect arguments). (Dmitry)
   . Fixed bug #77317 (__DIR__, __FILE__, realpath() reveal physical path for
     subst virtual drive). (Anatol)