Fix error on comparing git.Remote

[tzing]

We can't use 'foo' in repo.remotes syntax in current version, but 'foo' in repo.refs works fine.

It raises AttributeError before it runs full name search:

In [2]: r = git.Repo('.')

In [3]: 'origin' in r.remotes
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-3-800621fb1c9b> in <module>
----> 1 'origin' in r.remotes

~/Projects/GitPython/git/util.py in __contains__(self, attr)
    865     def __contains__(self, attr):
    866         # first try identity match for performance
--> 867         rval = list.__contains__(self, attr)
    868         if rval:
    869             return rval

~/Projects/GitPython/git/remote.py in __eq__(self, other)
    449
    450     def __eq__(self, other):
--> 451         return self.name == other.name
    452
    453     def __ne__(self, other):

AttributeError: 'str' object has no attribute 'name'

fix it add type check before it compares name.

[codecov-io]

Codecov Report

Merging #839 into master will decrease coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #839      +/-   ##
==========================================
- Coverage   94.79%   94.67%   -0.13%     
==========================================
  Files          59       59              
  Lines        9603     9386     -217     
==========================================
- Hits         9103     8886     -217     
  Misses        500      500

Impacted Files	Coverage Δ
git/objects/tree.py	59.64% <0%> (-0.93%)	⬇️
git/index/util.py	90.69% <0%> (-0.61%)	⬇️
git/index/typ.py	96.82% <0%> (-0.58%)	⬇️
git/refs/log.py	93.84% <0%> (-0.53%)	⬇️
git/objects/base.py	95.83% <0%> (-0.33%)	⬇️
git/refs/tag.py	96.66% <0%> (-0.31%)	⬇️
git/test/lib/helper.py	91.86% <0%> (-0.28%)	⬇️
git/refs/reference.py	95.74% <0%> (-0.26%)	⬇️
git/objects/commit.py	91.59% <0%> (-0.25%)	⬇️
git/cmd.py	83.83% <0%> (-0.18%)	⬇️
... and 26 more

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[Byron]

My apologies for the late reply - I must have missed this PR :(!
Thanks a lot for your contribution!