CI: bootstraps: append +apt-android-7 to bootstrap archives

When they are generated from master branch.  This is done since
termux-app now comes in two flavours, one for android >= 5 and one for
android >= 7.

.github/workflows/bootstrap_archives.yml

@@ -56,7 +56,7 @@ jobs:
           else
             tag_rev=1
           fi
-          new_tag="${new_tag}-r${tag_rev}"
+          new_tag="${new_tag}-r${tag_rev}+apt-android-7"
           git tag "$new_tag"
           git push --tags
           echo "::set-output name=tag_name::$new_tag"