pg_upgrade/test.sh: Quote sed(1) argument

Lack of quotes results in failure to run the test under older Solaris.

Author: Marina Polyakova, Victor Wagner
Discussion: https://postgr.es/m/feba89f89e8925b3535cb7d72b9e05e1@postgrespro.ru

src/bin/pg_upgrade/test.sh

@@ -33,7 +33,7 @@ standard_initdb() {
 
 # What flavor of host are we on?
 # Treat MINGW* (msys1) and MSYS* (msys2) the same.
-testhost=`uname -s | sed s/^MSYS/MINGW/`
+testhost=`uname -s | sed 's/^MSYS/MINGW/'`
 
 # Establish how the server will listen for connections
 case $testhost in