fix self-assign warning and drop from no-error list
Fixes a clang warning for self-assign
Also drops the -Wno-error=self-assign from CI debian-clang
A continuation of !14252 (merged). Split out to a separate MR not mess up the already review serie in that MR.
I am also not 100% that my local compile is identical to the CI. I tried to read from the gitlab-ci.yml and configured this build:
CC=clang CXX=clang++ meson build -Dgallium-drivers="iris,nouveau,kmsro,r300,r600,freedreno,swrast,svga,v3d,vc4,virgl,etnaviv,panfrost,lima,zink,radeonsi,tegra,d3d12,crocus" -Dvulkan-drivers="intel,amd,freedreno,broadcom,virtio-experimental" -Dglvnd=true