[R] Make "Can read Parquet files from a URL" less flaky

[HyukjinKwon]

Describe the enhancement requested

It fails (https://github.com/apache/arrow/actions/runs/20588184178/job/59128314858?pr=48688) with:

══ Warnings ════════════════════════════════════════════════════════════════════
── Warning ('test-parquet.R:481:3'): Can read Parquet files from a URL ─────────
downloaded length 0 != reported length 55136
Backtrace:
    ▆
 1. └─arrow::read_parquet(parquet_url) at test-parquet.R:481:3
 2.   └─arrow:::make_readable_file(file, mmap = mmap)
 3.     └─utils::download.file(file, tf, quiet = TRUE, mode = "wb")
── Warning ('test-parquet.R:481:3'): Can read Parquet files from a URL ─────────
cannot open URL 'https://github.com/apache/arrow/blob/64f2cc7986ce672dd1a8cb268d193617a80a1653/r/inst/v0.7.1.parquet?raw=true': HTTP status was '503 Service Unavailable'
Backtrace:
    ▆
 1. └─arrow::read_parquet(parquet_url) at test-parquet.R:481:3
 2.   └─arrow:::make_readable_file(file, mmap = mmap)
 3.     └─utils::download.file(file, tf, quiet = TRUE, mode = "wb")

══ Failed tests ════════════════════════════════════════════════════════════════
── Error ('test-parquet.R:481:3'): Can read Parquet files from a URL ───────────
Error in `download.file(file, tf, quiet = TRUE, mode = "wb")`: cannot open URL 'https://github.com/apache/arrow/blob/64f2cc7986ce672dd1a8cb268d193617a80a1653/r/inst/v0.7.1.parquet?raw=true'
Backtrace:
    ▆
 1. └─arrow::read_parquet(parquet_url) at test-parquet.R:481:3
 2.   └─arrow:::make_readable_file(file, mmap = mmap)
 3.     └─utils::download.file(file, tf, quiet = TRUE, mode = "wb")

[ FAIL 1 | WARN 2 | SKIP 24 | PASS 8435 ]

Component(s)

R