This updates our src/secp256k1 subtree to the lastest upstream master. Notable changes:
- New schnorrsig API (https://github.com/bitcoin-core/secp256k1/pull/844), which adds support for variable-length messages (not used in BIP341/342 transaction signing, so not relevant for us, but it changes the API, and makes some other simplifications). Some of our call sites had to be adapted.
- Don’t use asm optimizations for
gen_context
(https://github.com/bitcoin-core/secp256k1/pull/965). This fixes #22441. - Various testing/CI improvements