Fix PR creation (#908)

Author: dsyme

pkg/workflow/git_patch.go

@@ -62,8 +62,10 @@ func (c *Compiler) generateGitPatchStep(yaml *strings.Builder) {
 	yaml.WriteString("              else\n")
 	yaml.WriteString("                echo \"origin/$BRANCH_NAME does not exist, using merge-base with default branch\"\n")
 	yaml.WriteString("                # Get the default branch name\n")
-	yaml.WriteString("                DEFAULT_BRANCH=$(git symbolic-ref refs/remotes/origin/HEAD | sed 's@^refs/remotes/origin/@@')\n")
+	yaml.WriteString("                DEFAULT_BRANCH=\"${{ github.event.repository.default_branch }}\"\n")
 	yaml.WriteString("                echo \"Default branch: $DEFAULT_BRANCH\"\n")
+	yaml.WriteString("                # Fetch the default branch to ensure it's available locally\n")
+	yaml.WriteString("                git fetch origin $DEFAULT_BRANCH\n")
 	yaml.WriteString("                # Find merge base between default branch and current branch\n")
 	yaml.WriteString("                BASE_REF=$(git merge-base origin/$DEFAULT_BRANCH $BRANCH_NAME)\n")
 	yaml.WriteString("                echo \"Using merge-base as base: $BASE_REF\"\n")