doc: Fix doc comment for GstChildProxy

This removes warning like:

../subprojects/gstreamer/gst/gstchildproxy.h:57: Error: Gst: identifier not found on the first line:
   * #GstChildProxyInterface::get_child_by_name:
     ^

Part-of: <gstreamer/gstreamer!1297>
25 jobs for !1297 with child-proxy-doc-fix in 54 minutes and 2 seconds (queued for 6 seconds)
merge request
Name Stage Failure
failed
check fedora Test
Running with gitlab-runner 14.3.2 (e0218c92)
on gst-htz-3 z2CifdYy

Preparing the "docker" executor
Using Docker executor with image registry.freedesktop.org/ndufresne/gstreamer/amd64/fedora:2021-10-05.0-main ...
Authenticating with credentials from job payload (GitLab Registry)

Pulling docker image registry.freedesktop.org/ndufresne/gstreamer/amd64/fedora:2021-10-05.0-main ...

WARNING: Failed to pull image with policy "always": Error response from daemon: Get "https://registry.freedesktop.org/v2/": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers) (manager.go:214:20s)
ERROR: Job failed: failed to pull image "registry.freedesktop.org/ndufresne/gstreamer/amd64/fedora:2021-10-05.0-main" with specified policies [always]: Error response from daemon: Get "https://registry.freedesktop.org/v2/": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers) (manager.go:214:20s)

failed
integration testsuites fedora 1/4 Test
Running with gitlab-runner 14.3.2 (e0218c92)
on gst-htz-3 z2CifdYy

Preparing the "docker" executor
Using Docker executor with image registry.freedesktop.org/ndufresne/gstreamer/amd64/fedora:2021-10-05.0-main ...
Authenticating with credentials from job payload (GitLab Registry)

Pulling docker image registry.freedesktop.org/ndufresne/gstreamer/amd64/fedora:2021-10-05.0-main ...

WARNING: Failed to pull image with policy "always": Error response from daemon: Get "https://registry.freedesktop.org/v2/": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers) (manager.go:214:29s)
ERROR: Job failed: failed to pull image "registry.freedesktop.org/ndufresne/gstreamer/amd64/fedora:2021-10-05.0-main" with specified policies [always]: Error response from daemon: Get "https://registry.freedesktop.org/v2/": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers) (manager.go:214:29s)