[PATCH] Add a gitlab-ci stage to test for tabs in C source code.

This is just a simple test using perl (which is already required for
the build).
---
 My perl-fu is weak, and I'm sure there is a much slicker way to do
 this.  However, this is simple and seems to work for now.

 .gitlab-ci.yml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index d2416d1d..6aa14130 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -2,6 +2,7 @@ image: registry.gitlab.com/muttmua/mutt/ubuntu:18.04
 
 stages:
   - shellcheck
+  - tabcheck
   # - pylint
   - build
   - deploy
@@ -11,6 +12,11 @@ shellcheck:
   script:
     - (find . -name \*.sh && echo "gen_defs muttbug prepare") | xargs shellcheck --exclude=SC2003,SC2006,SC2086,SC2162,SC2046
 
+tabcheck:
+  stage: tabcheck
+  script:
+    - find . -name '*.[ch]' -print0 | xargs -0 perl -n -e '/\t/ && die "tab found in $ARGV"'
+
 # pylint:
 #   stage: pylint
 #   image: python:3.8-slim
-- 
2.52.0