Generally clean up a few things.

.github/actions/build-with-patched-std/action.yml

@@ -21,7 +21,7 @@ outputs:
     description: The size in bytes of the built test binary
     value: ${{ steps.measure.outputs.test-binary-size }}
 runs:
-  using: "composite"
+  using: composite
   steps:
     - shell: bash
       id: measure

.github/workflows/check-binary-size.yml

@@ -50,6 +50,8 @@ jobs:
       - name: Set up std repository and backtrace submodule for size test
         shell: bash
         working-directory: ${{ env.RUSTC_DIR }}
+        env:
+          PR_SOURCE_REPO: ${{ github.event.pull_request.head.repo.full_name }}
         run: |
           # Bootstrap config
           cat <<EOF > config.toml
@@ -69,19 +71,19 @@ jobs:
           git submodule update --init library/backtrace
 
           cd library/backtrace
-          git remote add head-pr https://github.com/${{ github.event.pull_request.head.repo.full_name }}
+          git remote add head-pr "https://github.com/$PR_SOURCE_REPO"
           git fetch --all
       - name: Build binary with base version of backtrace
         uses: ./backtrace/.github/actions/build-with-patched-std
         with:
-          backtrace-commit: $BASE_COMMIT
+          backtrace-commit: ${{ env.BASE_COMMIT }}
           main-rs: ${{ env.TEST_MAIN_RS }}
           rustc-dir: ${{ env.RUSTC_DIR }}
         id: size-reference
       - name: Build binary with PR version of backtrace
         uses: ./backtrace/.github/actions/build-with-patched-std
         with:
-          backtrace-commit: $HEAD_COMMIT
+          backtrace-commit: ${{ env.HEAD_COMMIT }}
           main-rs: ${{ env.TEST_MAIN_RS }}
           rustc-dir: ${{ env.RUSTC_DIR }}
         id: size-updated