Add a more readable diff in the PR description

The diff mainly consist in a single long line of keywords where new
keywords are added and old keywords may be removed.  Reviewing this is
a pain.

Generate a readable diff in the PR body for easily spotting issues.

Author: smortex

.github/workflows/upgrade.yml

@@ -46,11 +46,20 @@ jobs:
             if [ $EXISTING_PR -eq 0 ]
             then
               TITLE="syslog-ng-cfg-helper: $VERSION"
-              BODY="Generate from https://pypi.org/project/syslog-ng-cfg-helper/$VERSION"
+              BODY=$(mktemp)
+              echo "Generated from https://pypi.org/project/syslog-ng-cfg-helper/$VERSION" > $BODY
+              echo >> $BODY
+              echo 'For your convenience, here is a human-readable diff of the change:' >> $BODY
+              echo '```diff' >> $BODY
+              set +e
+              diff -u --label a/syntax/syslog-ng.vim <(git diff syntax/syslog-ng.vim | grep '^-syn keyword' | tr ' ' '\n' | tail -n +3) \
+                      --label b/syntax/syslog-ng.vim <(git diff syntax/syslog-ng.vim | grep '^+syn keyword' | tr ' ' '\n' | tail -n +3) >> $BODY
+              set -e
+              echo '```' >> $BODY
               git switch -c "$BRANCH"
               git commit -a -s -m "$TITLE"
               git push --force origin "$BRANCH"
-              gh pr create --title "$TITLE" --body "$BODY"
+              gh pr create --title "$TITLE" --body-file "$BODY"
             else
               echo "Pull Request already exists"
             fi