Dependabot ignore types/node major versions (#14362)

The `check-node-versions` script enforces that this package is kept in
sync with our Node major version, so we want dependabot to ignore major
version updates, but still allow smaller updates.

Note that we're still enforcing updates to the major version via the
aforementioned script; whenever Node is incremented by a major version,
the linter will require this package to be updated to that major
version too.

Note: We should technically ask dependabot to ignore 'minor' versions
too. It's currently set to 'major' because the latest node release
doesn't yet have types available for it (v22.18.0, latest types package
is v22.17.x). When it does, we can update this to ignore both major and
minor versions.

Author: JamieB-gu

.github/dependabot.yml

@@ -15,6 +15,12 @@ updates:
       - dependency-name: 'aws-cdk'
       - dependency-name: 'aws-cdk-lib'
       - dependency-name: 'constructs'
+      # The `check-node-versions` script enforces that this package is kept in
+      # sync with our Node major version, so we want dependabot to ignore major
+      # version updates, but still allow smaller updates.
+      - dependency-name: '@types/node'
+        update-types:
+          - 'version-update:semver-major'
 
     open-pull-requests-limit: 10
     groups: