ecpg: Add missing newline in meson.build

Noticed while performing a routine sanity check of the files in the
tree.  Issue introduced by 28f04984f0c2.

Discussion: https://postgr.es/m/CALa6HA4_Wu7-2PV0xv-Q84cT8eG7rTx6bdjUV0Pc=McAwkNMfQ@mail.gmail.com

src/interfaces/ecpg/preproc/meson.build

@@ -98,4 +98,4 @@ tests += {
     ],
     'deps': [ecpg_exe],
   },
-}
+}