Bump @actions/core from 1.2.3 to 1.2.6 in /build/actions (#12696)

Bumps [@actions/core](https://github.com/actions/toolkit/tree/HEAD/packages/core) from 1.2.3 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)

Signed-off-by: dependabot[bot] <support@github.com>

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

build/actions/package.json

@@ -15,7 +15,7 @@
 	"keywords": [],
 	"author": "",
 	"dependencies": {
-		"@actions/core": "^1.2.3",
+		"@actions/core": "^1.2.6",
 		"@actions/github": "^2.1.1",
 		"axios": "^0.19.2",
     "ts-node": "^8.6.2",