Drop python 3.6 (dependabot#7610)

This drops `python` `3.6` which has been EOL'd since Dec 2021.

This does _not_ tackle any of the follow-on work that dropping `3.6`
unlocks... ie, bumping to newer versions of `pip-tools`, `pip`, `poetry`
etc.

python/lib/dependabot/python/python_versions.rb

@@ -18,8 +18,6 @@ module PythonVersions
         3.9.17 3.9.16 3.9.15 3.9.14 3.9.13 3.9.12 3.9.11 3.9.10 3.9.9 3.9.8 3.9.7 3.9.6 3.9.5 3.9.4 3.9.2 3.9.1 3.9.0
         3.8.17 3.8.15 3.8.14 3.8.13 3.8.12 3.8.11 3.8.10 3.8.9 3.8.8 3.8.7 3.8.6 3.8.5 3.8.4 3.8.3 3.8.2 3.8.1 3.8.0
         3.7.17 3.7.15 3.7.14 3.7.13 3.7.12 3.7.11 3.7.10 3.7.9 3.7.8 3.7.7 3.7.6 3.7.5 3.7.4 3.7.3 3.7.2 3.7.1 3.7.0
-        3.6.15 3.6.14 3.6.13 3.6.12 3.6.11 3.6.10 3.6.9 3.6.8 3.6.7 3.6.6 3.6.5 3.6.4 3.6.3 3.6.2 3.6.1 3.6.0
-        3.5.10 3.5.8 3.5.7 3.5.6 3.5.5 3.5.4 3.5.3
       ).freeze
 
       # This list gets iterated through to find a valid version, so we have

python/spec/dependabot/python/update_checker/pip_version_resolver_spec.rb

@@ -81,16 +81,16 @@
       it { is_expected.to eq(Gem::Version.new("3.2.4")) }
 
       context "that is set to the oldest version of python supported by Dependabot" do
-        let(:python_version_content) { "3.5.3\n" }
-        it { is_expected.to eq(Gem::Version.new("2.2.24")) }
+        let(:python_version_content) { "3.7.0\n" }
+        it { is_expected.to eq(Gem::Version.new("3.2.4")) }
       end
 
       context "that is set to a python version no longer supported by Dependabot" do
-        let(:python_version_content) { "3.4.0\n" }
+        let(:python_version_content) { "3.6.0\n" }
         it "raises a helpful error" do
           expect { subject }.to raise_error(Dependabot::DependencyFileNotResolvable) do |err|
             expect(err.message).to start_with(
-              "Dependabot detected the following Python requirement for your project: '3.4.0'."
+              "Dependabot detected the following Python requirement for your project: '3.6.0'."
             )
           end
         end
@@ -126,17 +126,17 @@
       it { is_expected.to eq(Gem::Version.new("2.1.1")) }
 
       context "that is set to the oldest version of python supported by Dependabot" do
-        let(:python_version_content) { "3.5.3\n" }
+        let(:python_version_content) { "3.7.0\n" }
         it { is_expected.to eq(Gem::Version.new("2.1.1")) }
       end
 
       context "that is set to a python version no longer supported by Dependabot" do
-        let(:python_version_content) { "3.4.0\n" }
+        let(:python_version_content) { "3.6.0\n" }
 
         it "raises a helpful error" do
           expect { subject }.to raise_error(Dependabot::DependencyFileNotResolvable) do |err|
             expect(err.message).to start_with(
-              "Dependabot detected the following Python requirement for your project: '3.4.0'."
+              "Dependabot detected the following Python requirement for your project: '3.6.0'."
             )
           end
         end

python/spec/dependabot/python/update_checker_spec.rb

@@ -219,16 +219,16 @@
         it { is_expected.to eq(Gem::Version.new("3.2.4")) }
 
         context "that is set to the oldest version of python supported by Dependabot" do
-          let(:python_version_content) { "3.5.3\n" }
-          it { is_expected.to eq(Gem::Version.new("2.2.24")) }
+          let(:python_version_content) { "3.7.0\n" }
+          it { is_expected.to eq(Gem::Version.new("3.2.4")) }
         end
 
         context "that is set to a python version no longer supported by Dependabot" do
-          let(:python_version_content) { "3.4.0\n" }
+          let(:python_version_content) { "3.6.0\n" }
           it "raises a helpful error" do
             expect { subject }.to raise_error(Dependabot::DependencyFileNotResolvable) do |err|
               expect(err.message).to start_with(
-                "Dependabot detected the following Python requirement for your project: '3.4.0'."
+                "Dependabot detected the following Python requirement for your project: '3.6.0'."
               )
             end
           end