Fix PR viewer crash on older gh CLI versions

Remove closingIssuesReferences from gh pr view query fields since it is
not supported by older versions of the gh CLI, causing PR details to fail
with "Unknown JSON field" error. The linked_issues struct field already
has serde(default) so it gracefully falls back to an empty list.

Closes #576

Author: mehmetozguldev

crates/github/src/lib.rs

@@ -247,7 +247,7 @@ pub fn github_get_pr_details(
 
    let json_fields = "number,title,body,state,author,createdAt,updatedAt,isDraft,reviewDecision,\
                       url,headRefName,baseRefName,additions,deletions,changedFiles,commits,\
-                      statusCheckRollup,closingIssuesReferences,reviewRequests,mergeStateStatus,\
+                      statusCheckRollup,reviewRequests,mergeStateStatus,\
                       mergeable,labels,assignees";
 
    let output = gh_command(&app, Some(repo_dir))