Merge pull request from GHSA-7r3h-m5j6-3q42

* use uuid as our multiline env delimiter

* remove extra fn

* Fix version

* also throw error if delimiter is found in name or value

* move delimiter and uuid to global var in test

* upgrade uuid to newest version

* remove spy variable

* Update packages/core/src/core.ts

Co-authored-by: Thomas Boop <52323235+thboop@users.noreply.github.com>

* Update packages/core/src/core.ts

Co-authored-by: Thomas Boop <52323235+thboop@users.noreply.github.com>

RELEASES.md

@@ -1,5 +1,8 @@
 # @actions/core Releases
 
+### 1.9.1
+- Randomize delimiter when calling `core.exportVariable`
+
 ### 1.9.0
 - Added `toPosixPath`, `toWin32Path` and `toPlatformPath` utilities [#1102](https://github.com/actions/toolkit/pull/1102)