meson: pkgconfig difference

I think there is a tiny typo in src/interfaces/ecpg/ecpglib/meson.build:

diff --git a/src/interfaces/ecpg/ecpglib/meson.build 
b/src/interfaces/ecpg/ecpglib/meson.build
index dba9e3c3d9..da8d304f54 100644
--- a/src/interfaces/ecpg/ecpglib/meson.build
+++ b/src/interfaces/ecpg/ecpglib/meson.build
@@ -57,7 +57,7 @@ pkgconfig.generate(
    description: 'PostgreSQL libecpg library',
    url: pg_url,
    libraries: ecpglib_so,
-  libraries_private: [frontend_shlib_code, thread_dep],
+  libraries_private: [frontend_stlib_code, thread_dep],
    requires_private: ['libpgtypes', 'libpq'],
  )

This makes it match the other libraries.

Without this change, we get

Libs.private: ... -lpgport_shlib -lpgcommon_shlib

which seems wrong.