chore(deps): update urllib3 minimum version with environment markers (#1312)

Uses environment markers according to PEP 508. 

The current constraint expresses at least urllib3 version 1.10.0,
which has at least 5 CVEs open.

Projects relying on `sentry-sdk` will get an optimistic version of
the latest, so current test suites are already using the latest version
which patches these vulnerabilities.

Refs:

- GHSA-www2-v7xj-xrc6 (critical)
- GHSA-mh33-7rrq-662w (high)
- GHSA-hmv2-79q8-fv6g (high)
- GHSA-wqvq-5m8c-6g24 (moderate)
- GHSA-5phf-pp7p-vc2r (moderate)

Author: miketheman

setup.py

@@ -37,7 +37,12 @@ def get_file_text(file_name):
     package_data={"sentry_sdk": ["py.typed"]},
     zip_safe=False,
     license="BSD",
-    install_requires=["urllib3>=1.10.0", "certifi"],
+    install_requires=[
+        'urllib3>=1.25.7; python_version<="3.4"',
+        'urllib3>=1.26.9; python_version>="3.5"',
+        'urllib3>=1.26.11"; python_version >="3.6"',
+        "certifi",
+    ],
     extras_require={
         "flask": ["flask>=0.11", "blinker>=1.1"],
         "quart": ["quart>=0.16.1", "blinker>=1.1"],