github_tasks_macro.js

module.exports = async (params) => {
    const {app} = params;
    let file = app.workspace.getMostRecentLeaf()?.view?.file;
    if (!file) {
        return;
    }
    let frontmatter = app.metadataCache.getFileCache(file)?.frontmatter;
    let repo = frontmatter["gh-repo"]
    if (!repo) {
        return;
    }
    const url = `https://api.github.com/repos/${repo}/issues` 
    const text = await request({ url, method: "GET" });
    let issues = null;
    try {
        issues = JSON.parse(text)
    } catch (e) {
        return;
    }
    let fileContent = await app.vault.cachedRead(file)

    const marker = (number) => `gh${number}`
    return issues
        .filter(issue => fileContent.indexOf(marker(issue.number)) === -1)
        .map(issue => `- [ ] ([${marker(issue.number)}](${issue.html_url})) ${issue.title}`)
        .join('\n')
}

This is awesome, @amichuda! Thanks for sharing :D