Merge bitcoin/bitcoin#30703: test: Avoid duplicate curl call in get_previous_releases.py

fa5aeab3cb18405ecf8a1401d89539b924a618f6 test: Avoid duplicate curl call in get_previous_releases.py (MarcoFalke)

Pull request description:

  Seems odd having to translate `404` to "Binary tag was not found". Also, it seems odd to write a for-loop over a list with one item.

  Fix both issues by just using a single call to `curl --fail ...`.

  Can be tested with: `test/get_previous_releases.py -b v99.99.99`

  Before:

  ```
  Releases directory: releases
  Fetching: https://bitcoincore.org/bin/bitcoin-core-99.99.99/bitcoin-99.99.99-x86_64-linux-gnu.tar.gz
    % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                   Dload  Upload   Total   Spent    Left  Speed
    0  286k    0     0    0     0      0      0 --:--:--  0:00:01 --:--:--     0
  Binary tag was not found
  ```

  After:

  ```
  Releases directory: releases
  Fetching: https://bitcoincore.org/bin/bitcoin-core-99.99.99/bitcoin-99.99.99-x86_64-linux-gnu.tar.gz
    % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                   Dload  Upload   Total   Spent    Left  Speed
    0  286k    0     0    0     0      0      0 --:--:--  0:00:01 --:--:--     0
  curl: (22) The requested URL returned error: 404

ACKs for top commit:
  fanquake:
    ACK fa5aeab3cb18405ecf8a1401d89539b924a618f6
  brunoerg:
    utACK fa5aeab3cb18405ecf8a1401d89539b924a618f6
  tdb3:
    tested ACK fa5aeab3cb18405ecf8a1401d89539b924a618f6

Tree-SHA512: d5d31e0bccdd9de9b4a8ecf2e69348f4e8cee773050c8259b61db1ce5de73f6fbfffbe8c4d2571f7bef2de29cb42fd244573deebfbec614e487e76ef41681b9c

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