Replace textPlaceholder color usages with textSecondary (#3873)

* Replace `textPlaceholder` color usages with `textSecondary`

* Update screenshots

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Co-authored-by: ElementBot <android@element.io>

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/atomic/molecules/NumberedListMolecule.kt

@@ -41,7 +41,7 @@ fun NumberedListMolecule(
 private fun ItemNumber(
     index: Int,
 ) {
-    val color = ElementTheme.colors.textPlaceholder
+    val color = ElementTheme.colors.textSecondary
     Box(
         modifier = Modifier
             .border(1.dp, color, CircleShape)

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/theme/components/TextField.kt

@@ -200,7 +200,7 @@ private fun DecorationBox(
                     if (placeholder != null && isTextEmpty) {
                         Text(
                             text = placeholder,
-                            color = ElementTheme.colors.textPlaceholder,
+                            color = ElementTheme.colors.textSecondary,
                             style = ElementTheme.typography.fontBodyLgRegular,
                         )
                     }