Merge bitcoin/bitcoin#21860: [0.21] Backport update to Boost download URL

856de5bd5e4594d12c1d35704c49d0d086fc3d84 build,boost: update download url. (fdov)

Pull request description:

  Backports #21662 to the 0.21 branch. Boost has migrated it's download URLs due to bintrays imminent closure. The Boost site has also been updated to point to the new URLs. i.e: https://www.boost.org/users/history/version_1_70_0.html.

  Github-Pull: #21662
  Rebased-From: 36c10b9f4b181db6afa2f8cb7d4872b158768c16

ACKs for top commit:
  jarolrod:
    ACK 856de5bd5e4594d12c1d35704c49d0d086fc3d84

Tree-SHA512: cae7262f963dd6e00af699c3e1bce2ee3ff9f76c5dcc24c8a5bf37025b53de28e4cb80de65a380208ee1841a89736d5c35605e40b728b6c7a9f026d8165d74c8

Author: MarcoFalke

depends/packages/boost.mk

@@ -1,6 +1,6 @@
 package=boost
 $(package)_version=1_70_0
-$(package)_download_path=https://dl.bintray.com/boostorg/release/1.70.0/source/
+$(package)_download_path=https://boostorg.jfrog.io/artifactory/main/release/1.70.0/source/
 $(package)_file_name=boost_$($(package)_version).tar.bz2
 $(package)_sha256_hash=430ae8354789de4fd19ee52f3b1f739e1fba576f0aded0897c3c2bc00fb38778
 $(package)_patches=unused_var_in_process.patch