feat(gha/linux): upload deb packages for arm64 (#337)

We're still working on https://github.com/ooni/probe/issues/1466. The idea here is to teach the GH action for Linux to publish the debian package for arm64. When this is done, we can cleanup legacy build scripts and GH actions, because there is no remaining use case for them: we now build everything using the `./make` tool.

.github/workflows/debops-ci

@@ -304,8 +304,10 @@ def check_duplicate_package(pkgblock, packages_text):
     pname = li[0].split(" ", 1)[1]
     assert li[1].startswith("Version: "), li
     pver = li[1].split(" ", 1)[1]
+    assert li[2].startswith("Architecture: "), li
+    parch = li[2].split(" ", 1)[1]
 
-    m = f"Package: {pname}\nVersion: {pver}"
+    m = f"Package: {pname}\nVersion: {pver}\nArchitecture: {parch}"
     if m in packages_text:
         raise DuplicatePkgError()