meson: set correct install path for gdb helper

The original version of the patch used glib-2.0 but that was later changed
to gstreamer-1.0 for autotools. The meson file was forgotten.

Fix the path to match the one used in libgstreamer-gdb.py.in.
20 jobs for <span class="ref-name">meson-gdb</span> in 60 minutes and 32 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #293302
gst indent

00:01:02

passed #293301
manifest

00:00:44

 
  Build
passed #293303
build fedora x86_64

00:05:54

passed #293304
build nodebug fedora x86_64

00:05:48

 
  Test
passed #293305
check fedora

00:03:21

passed #293306
integration testsuites fedora

00:08:15

 
  Full Builds
passed #293308
build cerbero android universal

00:11:23

passed #293309
build cerbero cross win32

00:08:11

passed #293310
build cerbero cross win64

00:05:52

passed #293307
build cerbero fedora x86_64

00:06:56

 
  Full Tests
passed #293315
valgrind bad

00:04:36

passed #293312
valgrind base

00:12:34

passed #293387
valgrind core

00:11:55

passed #293316
valgrind ges

00:05:01

passed #293313
valgrind good

00:13:57

passed #293314
valgrind ugly

00:02:22

failed #293364
valgrind core

01:00:01

failed #293343
valgrind core

00:25:22

failed #293311
valgrind core

00:22:40

 
  Apps
passed #293317
android universal examples

00:08:02