Bump version of shiny to support bslib and align with teal's min shiny version (#1410)

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

Author: vedhav

DESCRIPTION

@@ -52,7 +52,7 @@ Imports:
     rmarkdown (>= 2.23),
     rtables (>= 0.6.11),
     scales (>= 1.4.0),
-    shiny (>= 1.6.0),
+    shiny (>= 1.8.1),
     shinyjs (>= 1.10.0),
     shinyvalidate (>= 0.1.3),
     shinyWidgets (>= 0.5.1),