doc: clarify text about internal module changes

Simplify phrasing for clarity and succinctness.

PR-URL: #22024
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/internal/readme.md

@@ -1,6 +1,6 @@
 # Internal Modules
 
 The modules in `lib/internal` are intended for internal use in Node.js core
-only, and are not accessible with `require()` from user modules. These are
-subject to change at **any** time. Reliance on these modules outside of core
+only, and are not accessible with `require()` from user modules. These modules
+can be changed at **any** time. Reliance on these modules outside of core
 is **not supported** in any way.