Extract dev script for running lintian (#1792)

Related #1716. Stacked on
#1791.

This PR pulls out the inlined `lintian` invocation to its own dev
script.

I had to apply one fix, because [shellcheck complained about `<(ls
*.deb)`, which should be `<(ls --
*.deb)`](https://www.shellcheck.net/wiki/SC2035).
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---------

Co-authored-by: Jan Heuermann <jan@jotaen.net>

.circleci/config.yml

@@ -194,17 +194,7 @@ jobs:
           command: lintian --version
       - run:
           name: Run lintian
-          command: |
-            set -exu
-            while read -r file; do
-              lintian \
-                --check \
-                --no-tag-display-limit \
-                --suppress-tags-from-file .lintianignore \
-                --no-cfg \
-                --fail-on warning,error \
-                "${file}"
-            done < <(ls *.deb)
+          command: ./dev-scripts/check-debian-pkg
   build_bundle:
     executor: python
     steps:

dev-scripts/check-debian-pkg

@@ -0,0 +1,22 @@
+#!/bin/bash
+
+# Perform static analysis on all .deb files in the working directory.
+
+# Exit on first failure.
+set -e
+
+# Echo commands before executing them, by default to stderr.
+set -x
+
+# Exit on unset variable.
+set -u
+
+while read -r file; do
+  lintian \
+    --check \
+    --no-tag-display-limit \
+    --suppress-tags-from-file .lintianignore \
+    --no-cfg \
+    --fail-on warning,error \
+    "${file}"
+done < <(ls -- *.deb)