Updated to-do to match guidance

We have standardized on to-do item and this
MR updates UI text to use that language
See the word list for details

ee/app/assets/javascripts/test_case_show/mixins/test_case_graphql.js

@@ -72,7 +72,7 @@ export default {
         });
     },
     /**
-     * We're using Public REST API to add Test Case as a Todo since
+     * We're using Public REST API to add Test Case as a to-do item since
      * GraphQL mutation to do the same is unavailable as of now.
      */
     addTestCaseAsTodo() {
@@ -83,7 +83,7 @@ export default {
         })
         .catch((error) => {
           createFlash({
-            message: s__('TestCases|Something went wrong while adding test case to Todo.'),
+            message: s__('TestCases|Something went wrong while adding test case to a to-do item.'),
             captureError: true,
             error,
           });
@@ -112,7 +112,9 @@ export default {
         })
         .catch((error) => {
           createFlash({
-            message: s__('TestCases|Something went wrong while marking test case todo as done.'),
+            message: s__(
+              'TestCases|Something went wrong while marking test case to-do item as done.',
+            ),
             captureError: true,
             error,
           });

ee/spec/frontend/test_case_show/mixins/test_case_graphql_spec.js

@@ -139,7 +139,7 @@ describe('TestCaseGraphQL Mixin', () => {
 
       return wrapper.vm.addTestCaseAsTodo().then(() => {
         expect(createFlash).toHaveBeenCalledWith({
-          message: 'Something went wrong while adding test case to Todo.',
+          message: 'Something went wrong while adding test case to a to-do item.',
           captureError: true,
           error: expect.any(Object),
         });
@@ -201,7 +201,7 @@ describe('TestCaseGraphQL Mixin', () => {
 
       return wrapper.vm.markTestCaseTodoDone().then(() => {
         expect(createFlash).toHaveBeenCalledWith({
-          message: 'Something went wrong while marking test case todo as done.',
+          message: 'Something went wrong while marking test case to-do item as done.',
           captureError: true,
           error: expect.any(Object),
         });

locale/gitlab.pot

@@ -33080,7 +33080,7 @@ msgstr ""
 msgid "TestCases|Search test cases"
 msgstr ""
 
-msgid "TestCases|Something went wrong while adding test case to Todo."
+msgid "TestCases|Something went wrong while adding test case to a to-do item."
 msgstr ""
 
 msgid "TestCases|Something went wrong while creating a test case."
@@ -33092,7 +33092,7 @@ msgstr ""
 msgid "TestCases|Something went wrong while fetching test cases list."
 msgstr ""
 
-msgid "TestCases|Something went wrong while marking test case todo as done."
+msgid "TestCases|Something went wrong while marking test case to-do item as done."
 msgstr ""
 
 msgid "TestCases|Something went wrong while moving test case."