Change action names

Author: ejsmith

.github/workflows/build-linux.yml

@@ -1,4 +1,4 @@
-name: Build
+name: Build Linux
 on: [push, pull_request]
 env:
   DOTNET_CLI_TELEMETRY_OPTOUT: 1

.github/workflows/build-osx.yml

@@ -1,4 +1,4 @@
-name: Build
+name: Build OSX
 on: [push, pull_request]
 env:
   DOTNET_CLI_TELEMETRY_OPTOUT: 1

.github/workflows/build-windows.yml

@@ -1,4 +1,4 @@
-name: Build
+name: Build Windows
 on: [push, pull_request]
 env:
   DOTNET_CLI_TELEMETRY_OPTOUT: 1