Restrict argument to isleapyear(::Integer) (#55317)

In 1.10 we have

```jl
julia> isleapyear(Year(1992))
false
```

which is semantically incorrect because `Year(1992)` is a duration (1992
years), not an instant. This PR restricts the currently unrestricted
argument to integers.

(cherry picked from commit fdecc59)

Author: jariji

stdlib/Dates/src/types.jl

@@ -203,7 +203,7 @@ function totaldays(y, m, d)
 end
 
 # If the year is divisible by 4, except for every 100 years, except for every 400 years
-isleapyear(y) = (y % 4 == 0) && ((y % 100 != 0) || (y % 400 == 0))
+isleapyear(y::Integer) = (y % 4 == 0) && ((y % 100 != 0) || (y % 400 == 0))
 
 # Number of days in month
 const DAYSINMONTH = (31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31)

stdlib/Dates/test/types.jl

@@ -41,6 +41,7 @@ end
     @test Dates.isleapyear(-1) == false
     @test Dates.isleapyear(4) == true
     @test Dates.isleapyear(-4) == true
+    @test_throws MethodError Dates.isleapyear(Dates.Year(1992))
 end
 # Create "test" check manually
 y = Dates.Year(1)