[Impeller] Fix a misspelling and name mismatch in a shader test fixture

impeller/fixtures/box_fade.frag

@@ -9,16 +9,16 @@ uniform FrameInfo {
 }
 frame_info;
 
-in vec2 interporlated_texture_coordinates;
+in vec2 interpolated_texture_coordinates;
 
 out vec4 frag_color;
 
 uniform sampler2D contents1;
 uniform sampler2D contents2;
 
 void main() {
-  vec4 tex1 = texture(contents1, interporlated_texture_coordinates);
-  vec4 tex2 = texture(contents2, interporlated_texture_coordinates);
+  vec4 tex1 = texture(contents1, interpolated_texture_coordinates);
+  vec4 tex2 = texture(contents2, interpolated_texture_coordinates);
   frag_color = mix(
       tex1, tex2,
       clamp(frame_info.cursor_position.x / frame_info.window_size.x, 0.0, 1.0));

impeller/fixtures/box_fade.vert

@@ -10,9 +10,9 @@ uniform_buffer;
 in vec3 vertex_position;
 in vec2 texture_coordinates;
 
-out vec2 interporlated_texture_coordinates;
+out vec2 interpolated_texture_coordinates;
 
 void main() {
   gl_Position = uniform_buffer.mvp * vec4(vertex_position, 1.0);
-  interporlated_texture_coordinates = texture_coordinates;
+  interpolated_texture_coordinates = texture_coordinates;
 }

impeller/fixtures/texture.frag

@@ -2,12 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-in vec2 interporlated_texture_coordinates;
+in vec2 interpolated_texture_coordinates;
 
 out vec4 frag_color;
 
 uniform sampler2D texture_contents;
 
 void main() {
-  frag_color = texture(texture_contents, interporlated_texture_coordinates);
+  frag_color = texture(texture_contents, interpolated_texture_coordinates);
 }