Auto merge of rust-lang#62757 - pietroalbini:fix-linuxtools, r=alexcrichton

ci: fix LinuxTools PR builder missing environment variables

This PR includes the new `public-credentials` variables group in PR builders, hopefully fixing sccache and toolstate.

~~Do not merge this yet as I want to do a test build first.~~

r? @alexcrichton
fixes rust-lang#62754 rust-lang#62753

Author: bors

.azure-pipelines/pr.yml

@@ -6,6 +6,9 @@ trigger: none
 pr:
 - master
 
+variables:
+- group: public-credentials
+
 jobs:
 - job: Linux
   timeoutInMinutes: 600