CI: Remove duplicated items from changelog (#346)

If the previous release's last commit was not a tagged commit (e.g.
runtime file update), the last commit was also listed in the bottom of
the new changelog.

Check the changelog of the previous release and extract the latest
commit id to avoid the duplication.

Author: k-takata

scripts/update-repo.sh

@@ -23,8 +23,15 @@ if [ ! -d vim/src ]; then
 	git submodule init
 fi
 git submodule update
-# get the last released tag name from this repo
-vimoldver=$(curl -s https://api.github.com/repos/vim/vim-win32-installer/releases/latest  | python -c 'import sys; from json import loads as l; print(l(sys.stdin.read())["tag_name"])')
+
+# get the last released commit id from this repo
+curl -s https://api.github.com/repos/vim/vim-win32-installer/releases/latest -o latest.json
+vimoldver=$(cat latest.json | python -c 'import sys; from json import loads as l; print(l(sys.stdin.read())["body"])' | sed -n -e '/.*(https:\/\/github\.com\/vim\/vim\/commit\/\([0-9a-f]*\)).*/{s//\1/;p;q}')
+if [ -z "$vimoldver" ]; then
+	# Fall back to the latest tag name
+	vimoldver=$(cat latest.json | python -c 'import sys; from json import loads as l; print(l(sys.stdin.read())["tag_name"])')
+fi
+rm latest.json
 
 # Get the latest vim source code
 cd vim