django_db_setup: warn instead of crash with teardown errors

[blueyed]

Previously it would cause pytest to crash, and this is just something to
warn about anyway.

Ref: django/channels#1091 (comment)

[codecov-io]

Codecov Report

Merging #726 into master will decrease coverage by 0.1%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #726      +/-   ##
==========================================
- Coverage      98%   97.89%   -0.11%     
==========================================
  Files          32       32              
  Lines        1853     1856       +3     
  Branches      147      147              
==========================================
+ Hits         1816     1817       +1     
- Misses         24       26       +2     
  Partials       13       13

Flag	Coverage Δ
#dj110	85.66% <50%> (-0.09%)	⬇️
#dj111	87.93% <50%> (-0.09%)	⬇️
#dj18	86.63% <50%> (-0.09%)	⬇️
#dj19	85.66% <50%> (-0.09%)	⬇️
#dj20	87.87% <50%> (-0.09%)	⬇️
#dj21	85.39% <50%> (-0.09%)	⬇️
#dj22	83.29% <50%> (-0.09%)	⬇️
#djmaster	81.3% <50%> (?)
#mysql_innodb	86.15% <50%> (-0.09%)	⬇️
#mysql_myisam	85.99% <50%> (-0.09%)	⬇️
#postgres	91.1% <50%> (-0.1%)	⬇️
#py27	90.94% <50%> (-0.1%)	⬇️
#py34	85.66% <50%> (-0.09%)	⬇️
#py35	85.66% <50%> (-0.09%)	⬇️
#py36	88.79% <50%> (+0.28%)	⬆️
#py37	85.77% <50%> (-0.09%)	⬇️
#pytest41	85.12% <50%> (-0.09%)	⬇️
#sqlite	90.3% <50%> (-0.1%)	⬇️
#sqlite_file	85.66% <50%> (-0.09%)	⬇️
#xdist	87.87% <50%> (-0.09%)	⬇️

Impacted Files	Coverage Δ
pytest_django/fixtures.py	96.29% <50%> (-1.02%)	⬇️

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[codecov-io]

Codecov Report

Merging #726 into master will decrease coverage by 0.1%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #726      +/-   ##
==========================================
- Coverage      98%   97.89%   -0.11%     
==========================================
  Files          32       32              
  Lines        1853     1856       +3     
  Branches      147      147              
==========================================
+ Hits         1816     1817       +1     
- Misses         24       26       +2     
  Partials       13       13

Flag	Coverage Δ
#dj110	85.66% <50%> (-0.09%)	⬇️
#dj111	87.93% <50%> (-0.09%)	⬇️
#dj18	86.63% <50%> (-0.09%)	⬇️
#dj19	85.66% <50%> (-0.09%)	⬇️
#dj20	87.87% <50%> (-0.09%)	⬇️
#dj21	85.39% <50%> (-0.09%)	⬇️
#dj22	83.29% <50%> (-0.09%)	⬇️
#djmaster	81.3% <50%> (?)
#mysql_innodb	86.15% <50%> (-0.09%)	⬇️
#mysql_myisam	85.99% <50%> (-0.09%)	⬇️
#postgres	91.1% <50%> (-0.1%)	⬇️
#py27	90.94% <50%> (-0.1%)	⬇️
#py34	85.66% <50%> (-0.09%)	⬇️
#py35	85.66% <50%> (-0.09%)	⬇️
#py36	88.79% <50%> (+0.28%)	⬆️
#py37	85.77% <50%> (-0.09%)	⬇️
#pytest41	85.12% <50%> (-0.09%)	⬇️
#sqlite	90.3% <50%> (-0.1%)	⬇️
#sqlite_file	85.66% <50%> (-0.09%)	⬇️
#xdist	87.87% <50%> (-0.09%)	⬇️

Impacted Files	Coverage Δ
pytest_django/fixtures.py	96.29% <50%> (-1.02%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 787bbec...b71c537. Read the comment docs.