Loosen dependency on backoff for newer Python versions

Author: hannseman

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; 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; python_version>='3.7'
 
 [options.extras_require]
 test =