chore: bump minimum Node version to 20.8.1

This bumps the minimum supported Node version to 20.8.1. Node 20 is the new LTS version
and some of our dependencies already dropped supported for Node 18.
Check out [our Node Support Policy](https://semantic-release.gitbook.io/semantic-release/support/node-support-policy)
to understand how we handle Node versions.

BREAKING CHANGE: Node 18 is not supported anymore. Users have to upgrade to Node 20.8.1 or later.

.github/workflows/test.yml

@@ -13,9 +13,9 @@ jobs:
     strategy:
       matrix:
         node-version:
-          - 18.17.0
-          - 20.6.1
+          - 20.8.1 # minimum supported Node version
           - 20
+          - 21
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1

package.json

@@ -21,7 +21,7 @@
     "prettier": "3.1.1"
   },
   "engines": {
-    "node": "^18.17 || >=20.6.1"
+    "node": ">=20.8.1"
   },
   "files": [
     "index.js"