Fix missing benchmark comparison in GitHub step summary

[NovemberZulu]

Description of changes:

Currently Detect regression step fail silently, see, e.g., #1151 , #1152, #1153. This happens because:

1. GitHub sets +e mode by default
2. Comparison apparently exists with non-zero error code of failure
3. This error code is propagated to the whole a=$(...) line
4. Shell exists at this point and if [ ! -z "$a" ]; then echo "${a}" >> $GITHUB_STEP_SUMMARY; exit 1; fi line isn't executed.

This PR is a simple fix that ensure that a=$(...) always exits with zero code.

Basic verification of bash behavior`

❯ bash
$ a=$(echo val1 && false)
$ echo $?
1
$ a=$(echo val2 && false || true)
$ echo $?
0
$ echo $a
val2

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.97%. Comparing base (3c1b6b1) to head (ee60d96).
⚠️ Report is 148 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1154      +/-   ##
============================================
+ Coverage     67.23%   67.97%   +0.74%     
- Complexity     5484     5624     +140     
============================================
  Files           159      160       +1     
  Lines         23025    23288     +263     
  Branches       4126     4176      +50     
============================================
+ Hits          15481    15831     +350     
+ Misses         6262     6164      -98     
- Partials       1282     1293      +11     

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