Fix oppia#5187 Textview contrast issue in locked lesson (oppia#5189)

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## Explanation
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Fixes oppia#5187, changing the background color of the locked lessons'
TextView fixed the contrast ratio issue.

## Essential Checklist
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- [x] The PR title and explanation each start with "Fix #bugnum: " (If
this PR fixes part of an issue, prefix the title with "Fix part of
#bugnum: ...".)
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[scripts/assets](https://github.com/oppia/oppia-android/tree/develop/scripts/assets)
files have their rationale included in the PR explanation.
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## For UI-specific PRs only

Before Fix

| Light Mode| Dark Mode|
|--------|--------|
|
![textcontrast](https://github.com/oppia/oppia-android/assets/76042077/01ffdf6c-3a20-4ce5-ab20-54ff7a82fedee)|![testdark](https://github.com/oppia/oppia-android/assets/76042077/d3f1fb3a-f267-4ced-9a00-3bdd67d4192a)|

After Fix

| Light Mode| Dark Mode|
|--------|--------|
|
![afterlight](https://github.com/oppia/oppia-android/assets/76042077/7d00b264-0bfb-4b35-8b99-b0b44ff7149d)|![lockbackground](https://github.com/oppia/oppia-android/assets/76042077/9147686c-e573-4285-aced-0af599d68d67)|

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- Add screenshots for portrait/landscape for both a tablet & phone of
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app/src/main/res/values-night/color_palette.xml

@@ -171,9 +171,9 @@
   <color name="color_palette_shared_card_border_stroke_color">@color/color_def_accessible_light_grey_2</color>
   <color name="color_palette_lesson_in_progress_chapter_index_background_color">@color/color_def_oppia_green</color>
   <color name="color_palette_lesson_in_progress_chapter_name_background_color">@color/color_def_accessible_grey</color>
-  <color name="color_palette_lessons_locked_chapter_container_background_color">@color/color_def_accessible_light_grey_2</color>
+  <color name="color_palette_lessons_locked_chapter_container_background_color">@color/color_def_accessible_light_grey</color>
   <color name="color_palette_lesson_locked_chapter_name_text_color">@color/color_def_white_80</color>
-  <color name="color_palette_lesson_locked_chapter_name_background_color">@color/color_def_accessible_light_grey_2</color>
+  <color name="color_palette_lesson_locked_chapter_name_background_color">@color/color_def_accessible_light_grey</color>
   <color name="color_palette_lessons_locked_vertical_divider_color">@color/color_def_dark_silver</color>
   <color name="color_palette_lesson_not_started_stroke_color">@color/color_def_white</color>
   <color name="color_palette_lesson_not_started_chapter_name_background_color">@color/color_def_oppia_green</color>

app/src/main/res/values/color_palette.xml

@@ -178,7 +178,7 @@
   <color name="color_palette_lesson_in_progress_chapter_name_background_color">@color/color_def_light_green</color>
   <color name="color_palette_lessons_locked_chapter_container_background_color">@color/color_def_accessible_light_grey_2</color>
   <color name="color_palette_lesson_locked_chapter_name_text_color">@color/color_def_accessible_light_grey_2</color>
-  <color name="color_palette_lesson_locked_chapter_name_background_color">@color/color_def_grey</color>
+  <color name="color_palette_lesson_locked_chapter_name_background_color">@color/color_def_oppia_grey_background</color>
   <color name="color_palette_lessons_locked_vertical_divider_color">@color/color_def_transparent</color>
   <color name="color_palette_lesson_not_started_stroke_color">@color/color_def_bright_green</color>
   <color name="color_palette_lesson_not_started_chapter_name_background_color">@color/color_def_white</color>