deps: bump @actions/core from 1.2.5 to 1.2.6 (#337)

Bumps [@actions/core](https://github.com/actions/toolkit/tree/HEAD/packages/core) from 1.2.5 to 1.2.6.
- [Release notes](https://github.com/actions/toolkit/releases)
- [Changelog](https://github.com/actions/toolkit/blob/main/packages/core/RELEASES.md)
- [Commits](https://github.com/actions/toolkit/commits/HEAD/packages/core)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

package.json

@@ -47,7 +47,7 @@
   },
   "homepage": "https://github.com/peaceiris/actions-mdbook#readme",
   "dependencies": {
-    "@actions/core": "^1.2.5",
+    "@actions/core": "^1.2.6",
     "@actions/exec": "^1.0.4",
     "@actions/io": "^1.0.2",
     "@actions/tool-cache": "^1.6.0",