Fixes literalWithCharPtrCompare cppcheck warnings

[rimbi]

The reason for the warning is the comparison of string literals like "ctid" with NULL, which appeared at 23 points as follows:

src/bin/pgcopydb/cli_list.c:1385:6: warning: String literal compared with variable 'NULL'. Did you intend to use strcmp() instead? [literalWithCharPtrCompare]
 if (streq(table->partKey, "ctid"))
     ^