Realtek firmware downloads from default source (linux-kernel) all fail. Partial failure from realtek-opensource.

```
(venv) a@b:~/Downloads/bumble/examples$ mkdir rtk_fws
(venv) a@b:~/Downloads/bumble/examples$ bumble-rtk-fw-download --output-dir rtk_fws/
Downloading
FROM: https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/rtl_bt
TO: rtk_fws
---
Failed to download rtl8723a_fw.bin: HTTP Error 403: Forbidden
---
Failed to download rtl8723b_fw.bin: HTTP Error 403: Forbidden
---
Failed to download rtl8723d_fw.bin: HTTP Error 403: Forbidden
---
Failed to download rtl8821a_fw.bin: HTTP Error 403: Forbidden
---
Failed to download rtl8821c_fw.bin: HTTP Error 403: Forbidden
---
Failed to download rtl8761a_fw.bin: HTTP Error 403: Forbidden
---
Failed to download rtl8761bu_fw.bin: HTTP Error 403: Forbidden
---
Failed to download rtl8822cu_fw.bin: HTTP Error 403: Forbidden
---
Failed to download rtl8822b_fw.bin: HTTP Error 403: Forbidden
---
Failed to download rtl8852au_fw.bin: HTTP Error 403: Forbidden
---
Failed to download rtl8852bu_fw.bin: HTTP Error 403: Forbidden
---
Failed to download rtl8852cu_fw.bin: HTTP Error 403: Forbidden
(venv) a@b:~/Downloads/bumble/examples$ git log -1
commit a275c399a3c2d321291e30fed5ff619dce124936 (HEAD -> main, origin/main, origin/HEAD)
Merge: c98275f 0b19347
Author: zxzxwu <92432172+zxzxwu@users.noreply.github.com>
Date: Thu Aug 7 16:52:17 2025 +0800

Merge pull request #734 from khsiao-google/le_subrating

Support LE Subrating
```

Partial failure from `--source realtek-opensource`

```
(venv) a@b:~/Downloads/bumble/examples$ bumble-rtk-fw-download --output-dir rtk_fws/ --source realtek-opensource
Downloading
FROM: https://github.com/Realtek-OpenSource/android_hardware_realtek/raw/rtk1395/bt/rtkbt/Firmware/BT
TO: rtk_fws
---
Downloaded rtl8723a_fw: 24452 bytes
---
Downloaded rtl8723b_fw: 45560 bytes
Downloaded rtl8723b_config: 10 bytes
---
Downloaded rtl8723d_fw: 49704 bytes
Downloaded rtl8723d_config: 6 bytes
---
Downloaded rtl8821a_fw: 40024 bytes
Downloaded rtl8821a_config: 10 bytes
---
Downloaded rtl8821c_fw: 44840 bytes
Downloaded rtl8821c_config: 6 bytes
---
Failed to download rtl8761a_fw.bin: HTTP Error 404: Not Found
---
Failed to download rtl8761bu_fw.bin: HTTP Error 404: Not Found
---
Failed to download rtl8822cu_fw.bin: HTTP Error 404: Not Found
---
Downloaded rtl8822b_fw: 51384 bytes
Downloaded rtl8822b_config: 6 bytes
---
Failed to download rtl8852au_fw.bin: HTTP Error 404: Not Found
---
Failed to download rtl8852bu_fw.bin: HTTP Error 404: Not Found
---
Failed to download rtl8852cu_fw.bin: HTTP Error 404: Not Found

```

And seeming success from `--source linux-from-scratch`

```
(venv) a@b:~/Downloads/bumble/examples$ bumble-rtk-fw-download --output-dir rtk_fws/ --source linux-from-scratch
Downloading
FROM: https://anduin.linuxfromscratch.org/sources/linux-firmware/rtl_bt
TO: rtk_fws
---
rtk_fws/rtl8723a_fw.bin already exists, skipping
---
rtk_fws/rtl8723b_fw.bin already exists, skipping
---
rtk_fws/rtl8723d_fw.bin already exists, skipping
---
rtk_fws/rtl8821a_fw.bin already exists, skipping
---
rtk_fws/rtl8821c_fw.bin already exists, skipping
---
Downloaded rtl8761a_fw.bin: 74488 bytes
No config available as rtl8761a_config.bin
---
Downloaded rtl8761bu_fw.bin: 44484 bytes
Downloaded rtl8761bu_config.bin: 6 bytes
---
Downloaded rtl8822cu_fw.bin: 60628 bytes
No config available as rtl8822cu_config.bin
---
rtk_fws/rtl8822b_fw.bin already exists, skipping
---
Downloaded rtl8852au_fw.bin: 67188 bytes
No config available as rtl8852au_config.bin
---
Downloaded rtl8852bu_fw.bin: 92933 bytes
No config available as rtl8852bu_config.bin
---
Downloaded rtl8852cu_fw.bin: 113336 bytes
No config available as rtl8852cu_config.bin

```