Use jq's IN() instead of index()

The end result is the same, but the construction is more ergonomic.

Dockerfile-curl.template

@@ -8,15 +8,15 @@ RUN set -eux; \
 		curl \
 		gnupg \
 		netbase \
-{{ if [
+{{ if env.codename | IN(
 	# we want versions of "sq" that contain https://gitlab.com/sequoia-pgp/sequoia/-/commit/b41e1504cd29097328cb21f95808c9972188499e (and thus "sq keyserver" subcommands; 0.26+)
 	# https://packages.debian.org/sq
 	"bullseye", # 0.24
 	# https://packages.ubuntu.com/sq
 	"jammy",    # 0.25
 	"focal",    # no sq
 	empty # trailing comma
-] | index(env.codename) then "" else ( -}}
+) then "" else ( -}}
 		sq \
 {{ ) end -}}
 		wget \

Dockerfile-scm.template

@@ -4,11 +4,7 @@ FROM buildpack-deps:{{ env.codename }}-curl
 RUN set -eux; \
 	apt-get update; \
 	apt-get install -y --no-install-recommends \
-{{
-if [
-	"focal", "groovy"
-] | index(env.codename) then (
--}}
+{{ if env.codename | IN("focal", "groovy") then ( -}}
 		bzr \
 {{ ) else "" end -}}
 		git \