Bump package version for post release

The 0.25.2 release had a number of packaging issues relating to CI and
versioning. This commit bumps the terra package version to 0.25.2.post0
which is a post-release notation that is pep440 compliant. The actual
version.txt file is not updated in this PR because we still want it to
show as 0.25.2 for `qiskit.__version__`, this is just a re-packaging of
the 0.25.2 release.

setup.py

@@ -59,7 +59,7 @@
 
 setup(
     name="qiskit-terra",
-    version="0.25.2",
+    version="0.25.2.post0",
     description="Software for developing quantum computing programs",
     long_description=README,
     long_description_content_type="text/markdown",