tools/fedora-worker-packer: set the commit sha

Currently the COMMIT_SHA variable is empty.

tools/appsre-build-fedora-worker-packer.sh

@@ -10,6 +10,7 @@ export BUILD_RPMS=false
 export SKIP_TAGS="rpmrepo_composer,rpmcopy,subscribe"
 FEDORA=fedora-38
 export PACKER_ONLY_EXCEPT=--only=amazon-ebs."$FEDORA"-x86_64,amazon-ebs."$FEDORA"-aarch64
+COMMIT_SHA="${COMMIT_SHA:-$(git rev-parse HEAD)}"
 
 # wait up to 30 minutes for the packit-as-a-service app (app id being 29076)
 for RETRY in {1..31}; do