tests: update wycheproof files

Wycheproof ownership was recently moved to C2SP
(https://github.com/C2SP/wycheproof). This PR updates all references to the new
URL and bumps to the latest version of the vector files.

This commit does not change the content of processed .h testvector files. To test:
```
make clean-testvectors testvectors
```

See: https://github.com/bitcoin-core/secp256k1/pull/1492#discussion_r1572443456

Co-authored-by: Sean Andersen <6730974+andozw@users.noreply.github.com>

src/wycheproof/WYCHEPROOF_COPYING

@@ -1,12 +1,12 @@
 * The file `ecdsa_secp256k1_sha256_bitcoin_test.json` in this directory
-  comes from Google's project Wycheproof with git commit
-  `b063b4aedae951c69df014cd25fa6d69ae9e8cb9`, see
-  https://github.com/google/wycheproof/blob/b063b4aedae951c69df014cd25fa6d69ae9e8cb9/testvectors_v1/ecdsa_secp256k1_sha256_bitcoin_test.json
+  comes from project Wycheproof with git commit
+  `df4e933efef449fc88af0c06e028d425d84a9495`, see
+  https://github.com/C2SP/wycheproof/blob/df4e933efef449fc88af0c06e028d425d84a9495/testvectors_v1/ecdsa_secp256k1_sha256_bitcoin_test.json
 
 * The file `ecdh_secp256k1_test.json` in this directory
-  comes from Google's project Wycheproof with git commit
-  `d9f6ec7d8bd8c96da05368999094e4a75ba5cb3d`, see
-  https://github.com/google/wycheproof/blob/d9f6ec7d8bd8c96da05368999094e4a75ba5cb3d/testvectors_v1/ecdh_secp256k1_test.json
+  comes from project Wycheproof with git commit
+  `df4e933efef449fc88af0c06e028d425d84a9495`, see
+  https://github.com/C2SP/wycheproof/blob/df4e933efef449fc88af0c06e028d425d84a9495/testvectors_v1/ecdh_secp256k1_test.json
 
 * The file `ecdsa_secp256k1_sha256_bitcoin_test.h` is generated from
   `ecdsa_secp256k1_sha256_bitcoin_test.json` using the script

src/wycheproof/ecdh_secp256k1_test.json

@@ -1,7 +1,6 @@
 {
   "algorithm" : "ECDH",
   "schema" : "ecdh_test_schema.json",
-  "generatorVersion" : "0.9rc5",
   "numberOfTests" : 752,
   "header" : [
     "Test vectors of type EcdhTest are intended for",
@@ -124,6 +123,10 @@
   "testGroups" : [
     {
       "type" : "EcdhTest",
+      "source" : {
+        "name" : "google-wycheproof",
+        "version" : "0.9rc5"
+      },
       "curve" : "secp256k1",
       "encoding" : "asn",
       "tests" : [

src/wycheproof/ecdsa_secp256k1_sha256_bitcoin_test.json

@@ -10,7 +10,7 @@
   "notes" : {
     "ArithmeticError" : {
       "bugType" : "EDGE_CASE",
-      "description" : "Some implementations of ECDSA have arithmetic errors that occur when intermediate results have extreme values. This test vector has been constructed to test such occurences.",
+      "description" : "Some implementations of ECDSA have arithmetic errors that occur when intermediate results have extreme values. This test vector has been constructed to test such occurrences.",
       "cves" : [
         "CVE-2017-18146"
       ]
@@ -95,7 +95,7 @@
     },
     "SignatureMalleabilityBitcoin" : {
       "bugType" : "SIGNATURE_MALLEABILITY",
-      "description" : "\"BitCoins\"-curves are curves where signature malleability can be a serious issue. An implementation should only accept a signature s where s < n/2. If an implementation is not meant for uses cases that require signature malleability then this implemenation should be tested with another set of test vectors.",
+      "description" : "\"BitCoins\"-curves are curves where signature malleability can be a serious issue. An implementation should only accept a signature s where s < n/2. If an implementation is not meant for uses cases that require signature malleability then this implementation should be tested with another set of test vectors.",
       "effect" : "In bitcoin exchanges, it may be used to make a double deposits or double withdrawals",
       "links" : [
         "https://en.bitcoin.it/wiki/Transaction_malleability",