ci: use Node v20 and enable strict engine checks (#303)

Strict engine checks are only for our CI - it doesn't impact consumers
of the actual package, but will ensure updates like #302 will fail CI

.github/workflows/checks.yaml

@@ -25,7 +25,7 @@ jobs:
           fetch-depth: 0
       - uses: actions/setup-node@v4
         with:
-          node-version: 18.x
+          node-version: 20.x
           cache: npm
       - name: install
         run: npm ci
@@ -49,7 +49,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: 18.x
+          node-version: 20.x
           cache: npm
 
       - run: npm ci
@@ -66,7 +66,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: 18.x
+          node-version: 20.x
           cache: npm
 
       - run: npm ci
@@ -82,7 +82,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: 18.x
+          node-version: 20.x
           cache: npm
 
       - run: npm ci

.github/workflows/release.yaml

@@ -16,7 +16,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: 18.x
+          node-version: 20.x
           cache: npm
 
       - name: install

.npmrc

@@ -0,0 +1 @@
+engine-strict=true