CI: replace nyc with c8 as coverage tool

Unclear if nyc is still actively maintained, and it does not seem
to work with ESM out of the box.

.gitignore

@@ -5,4 +5,4 @@ test/lib/
 test/typescript/definitions.js
 dist/
 openpgp.store/
-.nyc_output/
+coverage

package.json

@@ -54,7 +54,7 @@
     "browsertest": "npm start -- -o test/unittests.html",
     "test-browser": "karma start test/karma.conf.cjs",
     "test-browserstack": "karma start test/karma.conf.cjs --browsers bs_safari_latest,bs_ios_14,bs_safari_13_1",
-    "coverage": "nyc npm test",
+    "coverage": "c8 npm test",
     "lint": "eslint .",
     "docs": "jsdoc --configure .jsdocrc.cjs --destination docs --recurse README.md src && printf '%s' 'docs.openpgpjs.org' > docs/CNAME",
     "preversion": "rm -rf dist docs node_modules && npm ci && npm test",
@@ -63,8 +63,8 @@
   },
   "devDependencies": {
     "@openpgp/asmcrypto.js": "^3.0.0",
-    "@openpgp/noble-curves": "^1.2.1-0",
     "@openpgp/jsdoc": "^3.6.11",
+    "@openpgp/noble-curves": "^1.2.1-0",
     "@openpgp/noble-hashes": "^1.3.3-0",
     "@openpgp/seek-bzip": "^1.0.5-git",
     "@openpgp/tweetnacl": "^1.0.4-1",
@@ -79,6 +79,7 @@
     "argon2id": "^1.0.1",
     "benchmark": "^2.1.4",
     "bn.js": "^4.11.8",
+    "c8": "^8.0.1",
     "chai": "^4.3.7",
     "chai-as-promised": "^7.1.1",
     "eslint": "^8.34.0",
@@ -97,7 +98,6 @@
     "karma-mocha-reporter": "^2.2.5",
     "karma-webkit-launcher": "^2.1.0",
     "mocha": "^10.2.0",
-    "nyc": "^14.1.1",
     "playwright": "^1.30.0",
     "rollup": "^3.29.4",
     "sinon": "^15.1.0",