DEV: Correct typos and spelling mistakes (#12812)

Over the years we accrued many spelling mistakes in the code base. 

This PR attempts to fix spelling mistakes and typos in all areas of the code that are extremely safe to change 

- comments
- test descriptions
- other low risk areas

spec/models/username_validator_spec.rb

@@ -37,7 +37,7 @@ describe UsernameValidator do
                      error_message: I18n.t(:'user.username.short', min: 4))
     end
 
-    it 'is valid when the username has the minimum lenght' do
+    it 'is valid when the username has the minimum length' do
       SiteSetting.min_username_length = 4
 
       expect_valid('abcd')
@@ -50,7 +50,7 @@ describe UsernameValidator do
                      error_message: I18n.t(:'user.username.long', max: 8))
     end
 
-    it 'is valid when the username has the maximum lenght' do
+    it 'is valid when the username has the maximum length' do
       SiteSetting.max_username_length = 8
 
       expect_valid('abcdefgh')
@@ -122,7 +122,7 @@ describe UsernameValidator do
                        error_message: I18n.t(:'user.username.short', min: 3))
       end
 
-      it 'is valid when the username has the minimum lenght' do
+      it 'is valid when the username has the minimum length' do
         SiteSetting.min_username_length = 2
 
         expect_valid('পাখি', 'طائر')
@@ -135,7 +135,7 @@ describe UsernameValidator do
                        error_message: I18n.t(:'user.username.long', max: 8))
       end
 
-      it 'is valid when the username has the maximum lenght' do
+      it 'is valid when the username has the maximum length' do
         SiteSetting.max_username_length = 9
 
         expect_valid('Дровосек', 'چوب-لباسی', 'தமிழ்-தமிழ்')