ci: Add libc-dev for Ubuntu 26.04

.gitlab-ci.yml

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 872d45c..dc5b673 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1004,7 +1004,7 @@
   needs: [B-Trisquel11]
   before_script:
   - apt-get update -qq
-  - env DEBIAN_FRONTEND=noninteractive apt-get install -y -qq make gcc gtk-doc-tools texinfo
+  - env DEBIAN_FRONTEND=noninteractive apt-get install -y -qq make gcc libc-dev gtk-doc-tools texinfo
   script:
   - tar xfz out/b-trisquel11/*-*.tar.gz
   - cd $(tar tfz out/b-trisquel11/*-*.tar.gz | head -n1)
@@ -1018,7 +1018,7 @@
   needs: [B-Trisquel11]
   before_script:
   - apt-get update -qq
-  - env DEBIAN_FRONTEND=noninteractive apt-get install -y -qq make gcc gtk-doc-tools texinfo
+  - env DEBIAN_FRONTEND=noninteractive apt-get install -y -qq make gcc libc-dev gtk-doc-tools texinfo
   script:
   - tar xfz out/b-trisquel11/*-*.tar.gz
   - cd $(tar tfz out/b-trisquel11/*-*.tar.gz | head -n1)