maint: lowercase github workflow file

.github/workflows/build.yml

@@ -139,7 +139,7 @@ jobs:
           - Release
         arch:
           - x64
-          - ARM64
+          - arm64
         include:
           - configuration: Debug
             config: debug
@@ -147,7 +147,7 @@ jobs:
             config: release
           - arch: x64
             platform: x64
-          - arch: ARM64
+          - arch: arm64
             platform: arm64
     steps:
       - name: Check out files