build: disable Dependabot major jQuery version upgrades (#377)

WordPress currently relies upon jQuery 3.7.1. Ignore major version
bumps until the plan to upgrade to jQuery 4.0 lands in WordPress Core.

<!-- https://core.trac.wordpress.org/ticket/60478 -->

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dcalhoun

.github/dependabot.yml

@@ -11,3 +11,5 @@ updates:
             update-types: ['version-update:semver-major']
           - dependency-name: 'react-dom' # react@>=19.x.x blocked by https://github.com/WordPress/gutenberg/issues/71336
             update-types: ['version-update:semver-major']
+          - dependency-name: 'jquery' # jquery@>=4.x.x blocked by https://core.trac.wordpress.org/ticket/60478
+            update-types: ['version-update:semver-major']