fix: remove unintended conditional grouping causing overtriggering (#553)

Previously testing if an issue comment was a PR and if the comment
started with `/bench` were grouped in the same expression and evaluated
to true for every PR comment.

The ${{ }} expression syntax is optional in `if` conditionals, so I
removed it.  This wasn't caught initially as I always tested with
comments that started with `/bench`, and never with a comment that
shouldn't have triggered the benchmark.

Signed-off-by: Spencer Schrock <sschrock@google.com>

Author: spencerschrock

.github/workflows/bench.yml

@@ -8,7 +8,7 @@ permissions: {}
 
 jobs:
   publish-benchmark-container:
-    if: ${{ github.event_name == 'workflow_dispatch' }} || ${{ (github.event.issue.pull_request) && (startsWith(github.event.comment.body, '/bench')) }}
+    if: github.event_name == 'workflow_dispatch' || (github.event.issue.pull_request && startsWith(github.event.comment.body, '/bench'))
     runs-on: [ubuntu-latest]
     permissions:
       packages: write