Bump pbr from 5.2.0 to 5.2.1 (#5014)

Bumps [pbr](https://docs.openstack.org/pbr/latest/) from 5.2.0 to 5.2.1.

requirements/dev.txt

@@ -55,9 +55,9 @@ py==1.8.0 \
 
 # Required by mock
 funcsigs==1.0.2 --hash=sha256:330cc27ccbf7f1e992e69fef78261dc7c6569012cf397db8d3de0234e6c937ca
-pbr==5.2.0 \
-    --hash=sha256:6901995b9b686cb90cceba67a0f6d4d14ae003cd59bc12beb61549bdfbe3bc89 \
-    --hash=sha256:d950c64aeea5456bbd147468382a5bb77fe692c13c9f00f0219814ce5b642755
+pbr==5.2.1 \
+    --hash=sha256:0ce920b865091450bbcd452b35cf6d6eb8a6d9ce13ad2210d6e77557f85cf32b \
+    --hash=sha256:93d2dc6ee0c9af4dbc70bc1251d0e545a9910ca8863774761f92716dece400b6
 
 # Required by flake8
 entrypoints==0.3 --hash=sha256:589f874b313739ad35be6e0cd7efde2a4e9b6fea91edcc34e58ecbb8dbe56d19