pr-cve-check.yml: change distro to poky-altcfg

As greengrass-lite requires this and all build tests are changed to this distro.

(cherry picked from commit bdd05f5)

.github/workflows/pr-cve-check.yml

@@ -47,6 +47,7 @@ jobs:
           bitbake-layers add-layer ../meta-openembedded/meta-multimedia
           bitbake-layers add-layer ../meta-aws
           echo 'INHERIT += "cve-check"' >> conf/local.conf
+          echo DISTRO = \"poky-altcfg\" >> conf/local.conf
           bitbake -c cve_check `find ../meta-aws -name *.bb -type f  | sed 's!.*/!!' | sed 's!.bb!!' | sed 's!_.*!!' | sort | uniq | sed -z 's/\n/ /g'`
       - name: Show cve-summary.json
         run: |