doc: Replace characters that the PDF build cannot handle

A few characters in the acknowledgments list cannot be handled by the
PDF build, so replace with a similar ASCII character.

doc/src/sgml/release-14.sgml

@@ -4347,7 +4347,7 @@ Author: Fujii Masao <fujii@postgresql.org>
     <member>Michael Powers</member>
     <member>Michael Vastola</member>
     <member>Michail Nikolaev</member>
-    <member>Michał Albrycht</member>
+    <member>Michal Albrycht</member>
     <member>Mikael Gustavsson</member>
     <member>Movead Li</member>
     <member>Muhammad Usama</member>
@@ -4372,7 +4372,7 @@ Author: Fujii Masao <fujii@postgresql.org>
     <member>Odin Ugedal</member>
     <member>Oleg Bartunov</member>
     <member>Oleg Samoilov</member>
-    <member>Önder Kalacı</member>
+    <member>Önder Kalaci</member>
     <member>Pascal Legrand</member>
     <member>Paul Förster</member>
     <member>Paul Guo</member>