Backport of "wpesrc: fix some caps leaks using the non-GL output" into 1.18

Backport of !1618 (merged) "wpesrc: fix some caps leaks using the non-GL output".

Commits:

• b0033875 wpesrc: fix some caps leaks using the non-GL output

changed milestone to %1.18.1

restored source branch backport-mr-1618-into-1.18-wpesrc-caps-leaks

mentioned in merge request !1618 (merged)

mentioned in commit tpm/gst-plugins-bad@f4c467fa

added 7 commits

• 85b9e75d...dbef01af - 6 commits from branch gstreamer:1.18
• f4c467fa - wpesrc: fix some caps leaks using the non-GL output

Compare with previous version

merged