Add workflow permissions (#1334)

Resolves https://github.com/martincostello/dotnet-minimal-api-integration-testing/security/code-scanning/292.

Author: martincostello

.github/workflows/build.yml

@@ -22,11 +22,16 @@ env:
   NUGET_XMLDOC_MODE: skip
   TERM: xterm
 
+permissions: {}
+
 jobs:
   build:
     name: ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
 
+    permissions:
+      contents: read
+
     strategy:
       fail-fast: false
       matrix: