Update gruvbox color themes to support inlay hint (#6285)

The gruvbox themes (gruvbox, gruvbox dark hard and guvbox light)
don't provide a colour for the new virtual inlay hints. Looking at the
original repo, and other derivatives, there doesn't appear to be a clear
definition of what inlay hints should be. Although most sources indicate
that it can be the same as the color for comments.

Considering that, this commit sets the new field on each of the three
themes to be gray1, same as commented text.

Signed-off-by: Josh Bainbridge <josh.bainbridge@gmail.com>

runtime/themes/gruvbox.toml

@@ -60,6 +60,7 @@
 "ui.menu.selected" = { fg = "bg2", bg = "blue1", modifiers = ["bold"] }
 "ui.virtual.whitespace" = "bg2"
 "ui.virtual.ruler" = { bg = "bg1" }
+"ui.virtual.inlay-hint" = { fg = "gray1" }
 
 "diagnostic.warning" = { underline = { color = "orange1", style = "curl" } }
 "diagnostic.error" = { underline = { color = "red1", style = "curl" } }

runtime/themes/gruvbox_dark_hard.toml

@@ -66,6 +66,7 @@
 "ui.menu.selected" = { fg = "bg2", bg = "blue1", modifiers = ["bold"] }
 "ui.virtual.whitespace" = "bg2"
 "ui.virtual.ruler" = { bg = "bg1" }
+"ui.virtual.inlay-hint" = { fg = "gray1" }
 
 "markup.heading" = "aqua1"
 "markup.bold" = { modifiers = ["bold"] }

runtime/themes/gruvbox_light.toml

@@ -61,6 +61,7 @@
 "ui.menu.selected" = { fg = "bg2", bg = "blue1", modifiers = ["bold"] }
 "ui.virtual.whitespace" = "bg2"
 "ui.virtual.ruler" = { bg = "bg1" }
+"ui.virtual.inlay-hint" = { fg = "gray1" }
 
 "diagnostic.warning" = { underline = { color = "orange1", style = "curl" } }
 "diagnostic.error" = { underline = { color = "red1", style = "curl" } }