Update build badge in readme to show the build workflow status instead of test

[sequba]

Context

The badge in our readme file shows build: failing because of #1430. It is misleading because the build workflow works fine. It's only the browser tests that are broken.

This PR changes the badge to report the status of the build workflow instead of the test workflow.

Types of changes

• Breaking change (a fix or a feature because of which an existing functionality doesn't work as expected anymore)
• New feature or improvement (a non-breaking change that adds functionality)
• Bug fix (a non-breaking change that fixes an issue)
• Additional language file, or a change to an existing language file (translations)
• Change to the documentation

Checklist:

• I have reviewed the guidelines about Contributing to HyperFormula and I confirm that my code follows the code style of this project.
• I have signed the Contributor License Agreement.
• My change is compliant with the OpenDocument standard.
• My change is compatible with Microsoft Excel.
• My change is compatible with Google Sheets.
• I described my changes in the CHANGELOG.md file.
• My changes require a documentation update.
• My changes require a migration guide.

[github-actions]

Performance comparison of head (9d4ac52) vs base (67bae9e)

                                     testName |   base |   head | change
------------------------------------------------------------------------
                                      Sheet A | 515.48 | 518.98 | +0.68%
                                      Sheet B | 166.93 | 169.44 | +1.50%
                                      Sheet T | 147.84 | 149.42 | +1.07%
                                Column ranges | 514.89 | 526.32 | +2.22%
Sheet A:  change value, add/remove row/column |  15.33 |  16.03 | +4.57%
 Sheet B: change value, add/remove row/column | 133.09 | 137.52 | +3.33%
                   Column ranges - add column | 158.24 | 162.22 | +2.52%
                Column ranges - without batch | 458.63 | 479.33 | +4.51%
                        Column ranges - batch |  114.8 | 123.21 | +7.33%