Add bors environment to CI

This will be used to access secrets once we move off rust-lang-ci.

Author: Kobzol

.github/workflows/ci.yml

@@ -73,6 +73,15 @@ jobs:
     needs: [ calculate_matrix ]
     runs-on: "${{ matrix.os }}"
     timeout-minutes: 360
+    # The bors environment contains secrets required for elevated workflows (try and auto builds),
+    # which need to access e.g. S3 and upload artifacts. We want to provide access to that
+    # environment only on the try/auto branches, which are only accessible to bors.
+    # This also ensures that PR CI (which doesn't get write access to S3) works, as it cannot
+    # access the environment.
+    #
+    # We only enable the environment for the rust-lang/rust repository, so that rust-lang-ci/rust
+    # CI works until we migrate off it (since that repository doesn't contain the environment).
+    environment: ${{ ((github.repository == 'rust-lang/rust' && (github.ref == 'refs/heads/try' || github.ref == 'refs/heads/auto')) && 'bors') || '' }}
     env:
       CI_JOB_NAME: ${{ matrix.name }}
       CI_JOB_DOC_URL: ${{ matrix.doc_url }}