test: Change more contexts to describes for better sentences

- We could have added "to" to the `RSpec/ContextWording` list of valid
  `context` prefixes, but switching these to `describe` is less special.

Library/Homebrew/test/cask/dsl_spec.rb

@@ -168,37 +168,37 @@
         cask.config = config
       end
 
-      context "when it is 'zh'" do
+      describe "to 'zh'" do
         let(:languages) { ["zh"] }
 
         it { is_expected.to be_the_chinese_version }
       end
 
-      context "when it is 'zh-XX'" do
+      describe "to 'zh-XX'" do
         let(:languages) { ["zh-XX"] }
 
         it { is_expected.to be_the_chinese_version }
       end
 
-      context "when it is 'en'" do
+      describe "to 'en'" do
         let(:languages) { ["en"] }
 
         it { is_expected.to be_the_english_version }
       end
 
-      context "when it is 'xx-XX'" do
+      describe "to 'xx-XX'" do
         let(:languages) { ["xx-XX"] }
 
         it { is_expected.to be_the_english_version }
       end
 
-      context "when it is 'xx-XX,zh,en'" do
+      describe "to 'xx-XX,zh,en'" do
         let(:languages) { ["xx-XX", "zh", "en"] }
 
         it { is_expected.to be_the_chinese_version }
       end
 
-      context "when it is 'xx-XX,en-US,zh'" do
+      describe "to 'xx-XX,en-US,zh'" do
         let(:languages) { ["xx-XX", "en-US", "zh"] }
 
         it { is_expected.to be_the_english_version }

Library/Homebrew/test/os/mac/version_spec.rb

@@ -40,7 +40,7 @@
     expect(version).to be < Version.create("10.15")
   end
 
-  context "when after Big Sur" do
+  describe "after Big Sur" do
     specify "comparison with :big_sur" do
       expect(big_sur_major).to eq :big_sur
       expect(big_sur_major).to be <= :big_sur

Library/Homebrew/test/requirement_spec.rb

@@ -148,7 +148,7 @@
   end
 
   describe "#build?" do
-    context "when :build tag is specified" do
+    context "when the :build tag is specified" do
       subject { described_class.new([:build]) }
 
       it { is_expected.to be_a_build_requirement }