Gitblame: fix fatal error on chdir() when basepath is set and phpcs is run from subdir

The `Reporter::prepareFileReport()` method strips the `basepath` off the file name for the `$report['filename']`.

https://github.com/squizlabs/PHP_CodeSniffer/blob/276f68cc74a3e4e1855bab6d01f0089337d00ae0/src/Reporter.php#L337

While this is fine in most cases, for "blame" reports, the full path is needed.

This changes the path passed to the `getBlameContent()` method in subclasses of the `VersionControl` class to the full path, which fixes the fatal error for the `Gitblame` report (and probably similar/related errors in the `Hgblame` and the `Svnblame` reports, but I don't have any repos to test this on).

Fixes 3854

Author: jrfnl

src/Reports/VersionControl.php

@@ -40,7 +40,7 @@ abstract class VersionControl implements Report
      */
     public function generateFileReport($report, File $phpcsFile, $showSources=false, $width=80)
     {
-        $blames = $this->getBlameContent($report['filename']);
+        $blames = $this->getBlameContent($phpcsFile->getFilename());
 
         $authorCache = [];
         $praiseCache = [];