ci: Fetch sources from local mirror

I've created a mirror of the _gasket-driver_ Git repository, to ensure
it remains available, even if Google decides to remove it or GitHub is
temporarily unavailable.

ci/build.sh

@@ -15,7 +15,17 @@ git_rev=$(
 )
 curl -fL \
     -o gasket-driver-${git_rev}.tar.gz \
-    https://github.com/google/gasket-driver/archive/${git_rev}.tar.gz
+    https://git.pyrocufflink.net/dustin/gasket-driver/archive/${git_rev}.tar.gz
+
+# We're downloading the archive from our local mirror of upstream's repository,
+# just in case it goes away or becomes unavailable.  Unfortunately, Gitea
+# creates a slightly different archive layout than GitHub, so we need to fix it
+# up before passing it to `rpmbuild`.
+rm -rf src
+mkdir src
+tar -xzf gasket-driver-${git_rev}.tar.gz -C src
+mv src/gasket-driver src/gasket-driver-${git_rev}
+tar -cf gasket-driver-${git_rev}.tar.gz -C src gasket-driver-${git_rev}
 
 rpmbuild \
     -D "_topdir ${PWD}" \