bug#61340: 29.0.60; Extra space in xref buffer

[Juri Linkov <juri@linkov.net>]

This is a small problem and I didn't notice it until now when
there was an important distinction whether there is a space
character at the beginning of the line, and it was misleading
to see that xref wrongly says there is a leading space.
This is because currently xref output differs from grep and occur
where there is no space between colon and the text from file.
Here is the fix:

```
diff --git a/lisp/progmodes/xref.el b/lisp/progmodes/xref.el
index f01b8a1af18..6160f217afb 100644
--- a/lisp/progmodes/xref.el
+++ b/lisp/progmodes/xref.el
@@ -1108,7 +1108,7 @@ xref--insert-xrefs
                                    maximize (xref-location-line
                                              (xref-item-location xref)))
            for line-format = (and max-line
-                                  (format "%%%dd: " (1+ (floor (log max-line 10)))))
+                                  (format "%%%dd:" (1+ (floor (log max-line 10)))))
            with item-text-props = (list 'mouse-face 'highlight
                                         'keymap xref--button-map
                                         'help-echo
```