Bump version of shiny to support bslib and align with teal's min shiny version (#906)

Bump shiny version as per the discussion
insightsengineering/teal.widgets#312 (comment)

Author: vedhav

DESCRIPTION

@@ -26,7 +26,7 @@ Depends:
     ggmosaic (>= 0.3.0),
     ggplot2 (>= 3.4.0),
     R (>= 4.1),
-    shiny (>= 1.6.0),
+    shiny (>= 1.8.1),
     teal (>= 0.16.0.9008),
     teal.transform (>= 0.6.0.9002)
 Imports: