ref-manual: Fixed a typo for installing "python3-git"

Fixes [YOCTO #9712]

(From yocto-docs rev: 533412bc482f09ace57345733cb1f9494bb4b34c)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/usingpoky.xml

@@ -959,7 +959,7 @@
    $ pip3 install GitPython --user
                     </literallayout>
                     Alternatively, you can install
-                    <filename>python3-3</filename> using the appropriate
+                    <filename>python3-git</filename> using the appropriate
                     distribution package manager (e.g.
                     <filename>apt-get</filename>, <filename>dnf</filename>, or
                     <filename>zipper</filename>).