go/analysis/passes/slog: fix Group kv offset

The first argument to Group is a key, so its value in the kvFuncs
map should be 1, not zero.

The test was also calling Group wrong.

Change-Id: Iafb176b361d5fdc50c28cffe46f49dea29553c63
Reviewed-on: https://go-review.googlesource.com/c/tools/+/495976
Reviewed-by: Alan Donovan <[email protected]>
Run-TryBot: Jonathan Amsterdam <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
gopls-CI: kokoro <[email protected]>

Author: jba

go/analysis/passes/slog/slog.go

@@ -204,7 +204,7 @@ var kvFuncs = map[string]map[string]int{
 		"WarnCtx":  2,
 		"ErrorCtx": 2,
 		"Log":      3,
-		"Group":    0,
+		"Group":    1,
 	},
 	"Logger": map[string]int{
 		"Debug":    1,

go/analysis/passes/slog/testdata/src/a/a.go

@@ -143,7 +143,8 @@ func All() {
 
 	r.Add(1, 2) // want `slog.Record.Add arg "1" should be a string or a slog.Attr`
 
-	_ = slog.Group("a", 1, 2, 3) // want `slog.Group arg "2" should be a string or a slog.Attr`
+	_ = slog.Group("key", "a", 1, "b", 2)
+	_ = slog.Group("key", "a", 1, 2, 3) // want `slog.Group arg "2" should be a string or a slog.Attr`
 
 }