Make posix and msys2 shells consistent in CI

[ppigazzini]

In CI, it is typical for the process to halt immediately when an error is encountered. However, with our shell: bash {0} configuration, the process continues despite errors for posix shells.
This commit updates the behavior of posix and msys2 shells to ensure consistency in terms of pipeline exit codes and stop conditions. We adopt the most appropriate default behavior as recommended by the GitHub documentation.

Update the code that searches for the bench value in the git log:

• to be compatible with the new shell settings
• to retry the value from the first line that contains only the template and spaces/tabs/newlines

$ false | true
$ echo $?
1

Shell parameters in Github Actions:

- posix:
  - shell undefined  -> bash -e {0}
  - shell: bash      -> bash --noprofile --norc -eo pipefail {0}
- msys2:
  - shell: msys2 {0} -> bash -leo pipefail {0}

https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idstepsshell https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#exit-codes-and-error-action-preference https://github.com/msys2/setup-msys2/blob/main/main.js

closes #4653

No functional change