Removes several more refs to 3.8

Author: chalmerlowe

noxfile.py

@@ -32,7 +32,7 @@
 ISORT_VERSION = "isort==5.11.0"
 LINT_PATHS = ["docs", "db_dtypes", "tests", "noxfile.py", "setup.py"]
 
-DEFAULT_PYTHON_VERSION = "3.8"
+DEFAULT_PYTHON_VERSION = "3.9"
 
 UNIT_TEST_PYTHON_VERSIONS: List[str] = [
     "3.9",
@@ -54,7 +54,7 @@
 UNIT_TEST_EXTRAS: List[str] = []
 UNIT_TEST_EXTRAS_BY_PYTHON: Dict[str, List[str]] = {}
 
-SYSTEM_TEST_PYTHON_VERSIONS: List[str] = ["3.8"]
+SYSTEM_TEST_PYTHON_VERSIONS: List[str] = ["3.9"]
 SYSTEM_TEST_STANDARD_DEPENDENCIES: List[str] = [
     "mock",
     "pytest",

owlbot.py

@@ -28,7 +28,7 @@
 # Add templated files
 # ----------------------------------------------------------------------------
 templated_files = common.py_library(
-    system_test_python_versions=["3.8"],
+    system_test_python_versions=["3.9"],
     cov_level=100,
     intersphinx_dependencies={
         "pandas": "https://pandas.pydata.org/pandas-docs/stable/"

setup.py

@@ -75,6 +75,6 @@ def readme():
     ],
     platforms="Posix; MacOS X; Windows",
     install_requires=dependencies,
-    python_requires=">=3.7",
+    python_requires=">=3.8",
     tests_require=["pytest"],
 )