deps: expand supported pyarrow versions to v4

setup.py

@@ -47,10 +47,10 @@
         # grpc.Channel.close() method isn't added until 1.32.0.
         # https://github.com/grpc/grpc/pull/15254
         "grpcio >= 1.32.0, < 2.0dev",
-        "pyarrow >= 1.0.0, < 4.0dev",
+        "pyarrow >= 1.0.0, < 5.0dev",
     ],
-    "pandas": ["pandas>=0.23.0", "pyarrow >= 1.0.0, < 4.0dev"],
-    "bignumeric_type": ["pyarrow >= 3.0.0, < 4.0dev"],
+    "pandas": ["pandas>=0.23.0", "pyarrow >= 1.0.0, < 5.0dev"],
+    "bignumeric_type": ["pyarrow >= 3.0.0, < 5.0dev"],
     "tqdm": ["tqdm >= 4.7.4, <5.0.0dev"],
     "opentelemetry": [
         "opentelemetry-api >= 0.11b0",

testing/constraints-3.9.txt

@@ -0,0 +1,7 @@
+# This constraints file is used to make sure that the latest dependency versions
+# we claim to support in setup.py are indeed installed in test sessions in the most
+# recent Python version supported (3.9 at the time of writing - 2021-05-05).
+#
+# NOTE: Not comprehensive yet, will eventually be maintained semi-automatically by
+# the renovate bot.
+pyarrow>=4.0.0