creating missing diffs dir and optimize branch fetch

Signed-off-by: Vincenzo Scamporlino <[email protected]>

Author: vinzscam

.github/workflows/release.yml

@@ -99,10 +99,10 @@ jobs:
       - name: Create new diffs
         run: |
           mkdir diffs
+          git fetch origin release/$NEW_VERSION
           for version in $(curl -s https://raw.githubusercontent.com/backstage/upgrade-helper-diff/master/releases.json | jq -r 'to_entries | .[] | .value.createApp // .key'); do
             echo "Creating diffs between version $version and $NEW_VERSION"
             git fetch origin release/$version
-            git fetch origin release/$NEW_VERSION
             git diff -U1 origin/release/$version..origin/release/$NEW_VERSION > diffs/$version..$NEW_VERSION.diff
           done
       - name: Create new branch with diff files for release ${NEW_VERSION}
@@ -118,10 +118,11 @@ jobs:
         run: git checkout -b release-diff/v${RELEASE_VERSION}
       - name: Create new diffs for yarn plugin
         run: |
+          mkdir diffs
+          git fetch origin release/yarn-plugin/$RELEASE_VERSION
           for version in $(curl -s https://raw.githubusercontent.com/backstage/upgrade-helper-diff/master/releases-yarn-plugin.json | jq -r 'to_entries |.[] | .key'); do
             echo "Creating yarn-plugin diffs between version $version and $RELEASE_VERSION"
             git fetch origin release/yarn-plugin/$version
-            git fetch origin release/yarn-plugin/$RELEASE_VERSION
             git diff -U1 origin/release/yarn-plugin/$version..origin/release/yarn-plugin/$RELEASE_VERSION > diffs/$version..$RELEASE_VERSION.diff
           done
       - name: Push the changes