Specify explicit contents: read workflow permissions

Three CI workflows that need only `contents: read` permissions and
no other permissions did not have explicit permissions set, and
would therefore be given default permissions configured for the
repository, which might be more expansive than the workflows need.

It is recommended to set explicit workflow permissions [1]. This
does that, specifying permissions as `pythonpackage.yml` already
did, and closing three `actions/missing-workflow-permissions`
CodeQL alerts (new since #2032 enabled scanning of GHA workflows).

[1]: https://codeql.github.com/codeql-query-help/actions/actions-missing-workflow-permissions/

.github/workflows/alpine-test.yml

@@ -2,6 +2,9 @@ name: test-alpine
 
 on: [push, pull_request, workflow_dispatch]
 
+permissions:
+  contents: read
+
 jobs:
   test:
     runs-on: ubuntu-latest

.github/workflows/cygwin-test.yml

@@ -2,6 +2,9 @@ name: test-cygwin
 
 on: [push, pull_request, workflow_dispatch]
 
+permissions:
+  contents: read
+
 jobs:
   test:
     runs-on: windows-latest

.github/workflows/lint.yml

@@ -2,6 +2,9 @@ name: Lint
 
 on: [push, pull_request, workflow_dispatch]
 
+permissions:
+  contents: read
+
 jobs:
   lint:
     runs-on: ubuntu-latest