Further fixes to Xcode 12.5 support.

Test for [MTLDevice supportsBCTextureCompression] only when using Xcode 12 and above.
Use Xcode 12.5 in GitHub Actions CI.
Fix typos in comments.
diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index af46642..0a66e13 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -13,7 +13,7 @@
   build:
     strategy:
       matrix:
-        xcode: [ "12.4" ]
+        xcode: [ "12.5" ]
         platform: [ "macos", "maccat", "ios", "tvos" ]
         os: [ "macos-latest" ]
         upload_artifacts: [ true ]
diff --git a/MoltenVK/MoltenVK/Commands/MVKMTLResourceBindings.h b/MoltenVK/MoltenVK/Commands/MVKMTLResourceBindings.h
index 7431871..86e46f5 100644
--- a/MoltenVK/MoltenVK/Commands/MVKMTLResourceBindings.h
+++ b/MoltenVK/MoltenVK/Commands/MVKMTLResourceBindings.h
@@ -36,14 +36,14 @@
     bool isDirty = true;
 } MVKMTLTextureBinding;
 
-/** Describes a MTLSamplerState resource bindi MVKMTLSamplerStateBindingng. */
+/** Describes a MTLSamplerState resource binding. */
 typedef struct MVKMTLSamplerStateBinding {
     union { id<MTLSamplerState> mtlSamplerState = nil; id<MTLSamplerState> mtlResource; }; // aliases
     uint16_t index = 0;
     bool isDirty = true;
 } MVKMTLSamplerStateBinding;
 
-/** Describes  MVKMTLBufferBindinga MTLBuffer resource binding. */
+/** Describes  a MTLBuffer resource binding. */
 typedef struct MVKMTLBufferBinding {
     union { id<MTLBuffer> mtlBuffer = nil; id<MTLBuffer> mtlResource; const void* mtlBytes; }; // aliases
     VkDeviceSize offset = 0;
diff --git a/MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm b/MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm
index 5a3b8f0..ac2ddff 100644
--- a/MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm
+++ b/MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm
@@ -4167,10 +4167,12 @@
 }
 
 bool mvkSupportsBCTextureCompression(id<MTLDevice> mtlDevice) {
-#if MVK_MACOS && !MVK_MACCAT
+#if MVK_MACOS
+#if MVK_XCODE_12 && !MVK_MACCAT
 	if ([mtlDevice respondsToSelector: @selector(supportsBCTextureCompression)]) {
 		return mtlDevice.supportsBCTextureCompression;
 	}
+#endif
 	return true;
 #endif
 	return false;