Install file(1) in the Debian CI job so shlibdeps can run

cpack's CPACK_DEBIAN_PACKAGE_SHLIBDEPS runs dpkg-shlibdeps, which needs
the file utility to detect ELF binaries and derive the runtime libc
dependency. The slim CI image does not ship it, so packaging failed at
the cpack step. Add file to the job toolchain.

.gitea/workflows/release.yml

@@ -86,7 +86,7 @@ jobs:
         run: |
           apt-get update
           apt-get install -y --no-install-recommends \
-            cmake make gcc libc6-dev dpkg-dev \
+            cmake make gcc libc6-dev dpkg-dev file \
             gcc-mingw-w64-x86-64 ca-certificates curl
 
       - name: Configure