Fix a failing build, as ciso8601 is currently not pip-installable

[nils-braun]

Install ciso8601 as conda package, not via pip, because building the wheel for ciso8601 fails with

 gcc -pthread -DNDEBUG -O2 -fPIC -DCISO8601_VERSION=2.1.3 -I/usr/share/miniconda/envs/test/include -c module.c -o build/temp.linux-x86_64-3.7/module.o
  module.c: In function ‘_parse’:
  module.c:446:30: warning: implicit declaration of function ‘PyTimeZone_FromOffset’ [-Wimplicit-function-declaration]
    446 |                     tzinfo = PyTimeZone_FromOffset(delta);
        |                              ^~~~~~~~~~~~~~~~~~~~~
  module.c:446:28: warning: assignment to ‘PyObject *’ {aka ‘struct _object *’} from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
    446 |                     tzinfo = PyTimeZone_FromOffset(delta);
        |                            ^
  module.c: In function ‘PyInit_ciso8601’:
  module.c:562:11: error: ‘PyDateTime_TimeZone_UTC’ undeclared (first use in this function); did you mean ‘PyDateTime_Time’?
    562 |     utc = PyDateTime_TimeZone_UTC;
        |           ^~~~~~~~~~~~~~~~~~~~~~~
        |           PyDateTime_Time
  module.c:562:11: note: each undeclared identifier is reported only once for each function it appears in
  error: command 'gcc' failed with exit status 1
  ----------------------------------------
  ERROR: Failed building wheel for ciso8601

which is very similar to closeio/ciso8601#101 (it seems pyscopg or sqlalchemy are pulling in pypy as a dependency).

[codecov-commenter]

Codecov Report

Merging #192 (2eb8af1) into main (ecc3da3) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              main      #192   +/-   ##
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  Coverage   100.00%   100.00%           
=========================================
  Files           59        59           
  Lines         2282      2282           
  Branches       314       314           
=========================================
  Hits          2282      2282           

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