Increase height of the demos iframes

[sequba]

Context

• Increasing the height of the iframes to show the full preview of a demo.

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)
• [x] Change to the documentation

[github-actions[bot]]

Performance comparison of head (7f4c20a753a5fca764690df8dd9d8619ae10e8c4) vs base (31e3f611fb309be231642780f3a04ee2b094ac9c)

                                     testName |   base |   head | change
------------------------------------------------------------------------
                                      Sheet A | 555.07 | 536.25 | -3.39%
                                      Sheet B | 184.53 | 170.67 | -7.51%
                                      Sheet T | 158.86 | 152.32 | -4.12%
                                Column ranges | 566.37 | 552.18 | -2.51%
Sheet A:  change value, add/remove row/column |  15.71 |  14.41 | -8.27%
 Sheet B: change value, add/remove row/column | 152.99 | 139.99 | -8.50%
                   Column ranges - add column | 163.68 | 158.56 | -3.13%
                Column ranges - without batch |  483.2 | 472.48 | -2.22%
                        Column ranges - batch | 120.88 | 117.02 | -3.19%