Merge bitcoin-core/secp256k1#1409: ci: Move remained task from Cirrus to GitHub Actions

676ed8f ci: Move "C++ (public headers)" from Cirrus to GitHub Actions (Hennadii Stepanov)
61fc3a2 ci: Move "C++ -fpermissive..." from Cirrus to GitHub Actions (Hennadii Stepanov)
d51fb0a ci: Move "MSan" from Cirrus to GitHub Actions (Hennadii Stepanov)
c22ac27 ci: Move sanitizers task from Cirrus to GitHub Actions (Hennadii Stepanov)

Pull request description:

  This PR concludes the migration from Cirrus CI to GitHub Actions.

ACKs for top commit:
  real-or-random:
    ACK 676ed8f

Tree-SHA512: d8ea91a20297ff4c2c11a02c0a52f19413fde442c71e2e8b660737c09d62e55e4ae3f9bdbdeb0d967f6720a3dffa1566b7f94e0e32bcd490ac052819d5427c84

Author: real-or-random