fix create with github URL on windows

[gvilums]

What does this PR do?

Replaces some uses of zig stdlib accessat (which were running into unreachable) with bun.sys.existsAt.
Fixes #10183

How did you verify your code works?

Manual testing

[github-actions]

❌ @gvilums 10 files with test failures on bun-windows-x86_64-haswell

• test\cli\install\bun-create.test.ts 1 failing
• test\cli\install\bunx.test.ts 1 failing
• test\cli\install\registry\bun-install-registry.test.ts 15 failing
• test\integration\next-pages\test\dev-server-ssr-100.test.ts 1 failing
• test\integration\next-pages\test\dev-server.test.ts 1 failing
• test\integration\next-pages\test\next-build.test.ts 1 failing
• test\js\bun\shell\bunshell.test.ts 2 failing
• test\js\node\dns\node-dns.test.js 2 failing
• test\js\node\fs\fs.test.ts 1 failing
• test\js\web\workers\worker.test.ts 1 failing

View test output

^{#b6a75d33b8ee6a3299c948757e3f1651b4522be7}

[github-actions]

❌ @gvilums 3 files with test failures on bun-darwin-aarch64:

• test/js/bun/http/serve.test.ts 2 failing
• test/js/bun/spawn/spawn.test.ts 1 failing
• test/js/node/http2/node-http2.test.js 1 failing

View test output

^{#b6a75d33b8ee6a3299c948757e3f1651b4522be7}

[github-actions]

❌ @gvilums 4 files with test failures on bun-darwin-x64:

• test/js/bun/shell/leak.test.ts SIGTERM
• test/js/bun/spawn/spawn.test.ts 1 failing
• test/js/node/watch/fs.watchFile.test.ts 1 failing
• test/js/web/fetch/fetch.tls.test.ts 1 failing

View test output

^{#b6a75d33b8ee6a3299c948757e3f1651b4522be7}

[Jarred-Sumner]

thank you