tools: update sqlc version

sqlc has now an official dockerhub organization (sqlc). The old org was
the personal dev account, and new images are not uploaded there anymore.

It looks like they formed a company (Riza, Inc) and are dedicating 100%
of their time to the project (which is great news!)

[sqlc v1.21.0](sqlc-dev/sqlc#2709) has a bug
generating unvalid go code (files with unused imports) so we use v1.20.0

Author: positiveblue

scripts/gen_sqlc_docker.sh

@@ -16,4 +16,4 @@ docker run \
   -e UID=$UID \
   -v "$DIR/../:/build" \
   -w /build \
-  kjconroy/sqlc:1.18.0 generate
+  sqlc/sqlc:1.20.0 generate