Fix mistake in navbar-dark-contrast's default value (#782)

Co-authored-by: cpsievert <[email protected]>

Author: cpsievert

inst/lib/bs5/scss/_variables.scss

@@ -1224,7 +1224,7 @@ $navbar-light-contrast: if(
   var(--#{$prefix}emphasis-color-rgb)
 ) !default; // Deepest contrasting color for navbarPage(inverse = FALSE).
 $navbar-dark-contrast: if(
-  type-of($navbar-light-bg) == color,
+  type-of($navbar-dark-bg) == color,
   color-contrast($navbar-dark-bg),
   var(--#{$prefix}emphasis-color-rgb)
 ) !default; // Deepest contrasting color for navbarPage(inverse = TRUE).

tools/patches/021-add-navbar-bg-vars-bs5.patch

@@ -21,7 +21,7 @@ index 91bdbfdf..709feeb2 100644
 +  var(--#{$prefix}emphasis-color-rgb)
 +) !default; // Deepest contrasting color for navbarPage(inverse = FALSE).
 +$navbar-dark-contrast: if(
-+  type-of($navbar-light-bg) == color,
++  type-of($navbar-dark-bg) == color,
 +  color-contrast($navbar-dark-bg),
 +  var(--#{$prefix}emphasis-color-rgb)
 +) !default; // Deepest contrasting color for navbarPage(inverse = TRUE).