ci: run steps with bash and retry flaky downloads

The runner defaults to sh, but the version and release steps use bash
syntax. Downloads from GitHub now retry on any error (connection resets
broke run #2).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/build-deb.yml

@@ -10,6 +10,10 @@ concurrency:
   group: build-deb-${{ github.ref }}
   cancel-in-progress: true
 
+defaults:
+  run:
+    shell: bash  # the runner's default is sh; steps below use bash syntax
+
 env:
   GITEA_URL: https://code.lotusguild.org
   OWNER: LotusGuild
@@ -31,8 +35,11 @@ jobs:
           apt-get install -y -qq --no-install-recommends \
             debhelper devscripts lintian fakeroot bats tmux fzf jq curl ca-certificates xz-utils >/dev/null
           VER=v0.10.0
-          curl -fsSL "https://github.com/koalaman/shellcheck/releases/download/${VER}/shellcheck-${VER}.linux.x86_64.tar.xz" | tar -xJ
+          curl -fsSL --retry 5 --retry-delay 5 --retry-all-errors -o shellcheck.tar.xz \
+            "https://github.com/koalaman/shellcheck/releases/download/${VER}/shellcheck-${VER}.linux.x86_64.tar.xz"
+          tar -xJf shellcheck.tar.xz
           install "shellcheck-${VER}/shellcheck" /usr/local/bin/shellcheck
+          rm -rf shellcheck.tar.xz "shellcheck-${VER}"
           shellcheck --version | head -2
 
       - name: npm ci