Loosen dependency on backoff for newer Python versions

Author: hannseman

CHANGELOG.md

@@ -13,6 +13,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#2714](https://github.com/open-telemetry/opentelemetry-python/pull/2714))
 - narrow protobuf dependencies to exclude protobuf >= 4
   ([#2720](https://github.com/open-telemetry/opentelemetry-python/pull/2720))
+- Loosen dependency on `backoff` for newer Python versions
+  ([#2726](https://github.com/open-telemetry/opentelemetry-python/pull/2726))
 
 ## [1.12.0rc1-0.31b0](https://github.com/open-telemetry/opentelemetry-python/releases/tag/v1.12.0rc1-0.31b0) - 2022-05-17
 

exporter/opentelemetry-exporter-otlp-proto-grpc/setup.cfg

@@ -45,7 +45,8 @@ install_requires =
     opentelemetry-api ~= 1.3
     opentelemetry-sdk ~= 1.11
     opentelemetry-proto == 1.12.0rc1
-    backoff >= 1.10.0, < 2.0.0
+    backoff >= 1.10.0, < 2.0.0; python_version<'3.7'
+    backoff >= 1.10.0, < 3.0.0; python_version>='3.7'
 
 [options.extras_require]
 test =

exporter/opentelemetry-exporter-otlp-proto-http/setup.cfg

@@ -45,7 +45,8 @@ install_requires =
     opentelemetry-api ~= 1.3
     opentelemetry-sdk ~= 1.11
     opentelemetry-proto == 1.12.0rc1
-    backoff >= 1.10.0, < 2.0.0
+    backoff >= 1.10.0, < 2.0.0; python_version<'3.7'
+    backoff >= 1.10.0, < 3.0.0; python_version>='3.7'
 
 [options.extras_require]
 test =