Fix wgrep footer marking excluding last result from edits

[fabianfranzelin]

The previous code used (forward-line -1) after finding the 'rg finished' line, which moved point to the last result line and marked it as read-only footer. This caused wgrep to skip the last match during search-replace operations.

Fix by using (beginning-of-line) on the 'rg finished' line itself, so only that line and anything after it is marked as footer.

[dajva]

Thanks for the pr!
This makes all wgrep tests fail. Not sure why I can't trigger gh actions on this pr but you can run it yourself locally: https://rgel.readthedocs.io/en/latest/contribute.html

7 unexpected results:
   FAILED  rg-integration-test/wgrep-group
   FAILED  rg-integration-test/wgrep-group-align
   FAILED  rg-integration-test/wgrep-group-align-columns
   FAILED  rg-integration-test/wgrep-group-align-columns-custom-separators
   FAILED  rg-integration-test/wgrep-group-columns
   FAILED  rg-integration-test/wgrep-nogroup
   FAILED  rg-integration-test/wgrep-nogroup-columns

So not sure what environment you are running or if you triggered some edge case or something. As it stands now, I can't merge this as is. If you can provide more info on how this happens, ideally a self contained test case that shows this in a clean environment I can take a more thorough look at it.