fix: non-integers passed to str-slice

[skip libsass]

spec/core_functions/string/slice.hrx

@@ -377,13 +377,6 @@ Error: argument `$end-at` of `str-slice($string, $start-at, $end-at:-1)` must be
 
    ------^
 
-<===>
-================================================================================
-<===> error/decimal/options.yml
----
-:todo:
-- sass/libsass#2922
-
 <===>
 ================================================================================
 <===> error/decimal/start/input.scss
@@ -397,6 +390,14 @@ Error: 0.5 is not an int.
   '
   input.scss 1:7  root stylesheet
 
+<===> error/decimal/start/error-libsass
+Error: $start-at: 0.500000 is not an int
+        on line 1:7 of input.scss, in function `str-slice`
+        from line 1:7 of input.scss
+>> a {b: str-slice("", 0.5)}
+
+   ------^
+
 <===>
 ================================================================================
 <===> error/decimal/end/input.scss
@@ -410,6 +411,14 @@ Error: 1.5 is not an int.
   '
   input.scss 1:7  root stylesheet
 
+<===> error/decimal/end/error-libsass
+Error: $end-at: 1.500000 is not an int
+        on line 1:7 of input.scss, in function `str-slice`
+        from line 1:7 of input.scss
+>> a {b: str-slice("", 1, 1.5)}
+
+   ------^
+
 <===>
 ================================================================================
 <===> error/too_few_args/input.scss