chore: Split workflows and simplify testing (#67)

The CI workflow has been split into separate CI and PR workflows,
and the number of Terraform versions that are tested whenever changes
are made to the module has been reduced, Terraform uses semantic
versioning so we will only test against the latest major.minor versions.

.github/workflows/ci.yaml

@@ -1,15 +1,6 @@
 name: CI
 
 on:
-  pull_request:
-    branches:
-    - main
-    paths-ignore:
-    - .editorconfig
-    - .gitignore
-    - CHANGELOG.md
-    - LICENSE.md
-    - README.md
   push:
     branches:
     - main
@@ -18,6 +9,7 @@ on:
     - .gitignore
     - CHANGELOG.md
     - LICENSE.md
+    - Makefile
     - README.md
 
 jobs:
@@ -30,35 +22,17 @@ jobs:
     - name: Setup Terraform
       uses: hashicorp/setup-terraform@v3
       with:
-        terraform_version: ${{ matrix.terraform_version }}
+        terraform_version: "1.10"
     - name: Initialise with no backend
       run: terraform init -backend=false
     - name: Check formatting
       run: terraform fmt -check -recursive
     - name: Validate the configuration
       run: terraform validate
-    strategy:
-      matrix:
-        terraform_version: [ "1.0", "1.1", "1.2", "1.3", "1.4", "1.5", "1.6" ]
-
-  caller-identity:
-    if: ${{ github.event_name == 'push' }}
-    name: Return the IAM user
-    permissions:
-      contents: read
-      id-token: write
-    runs-on: ubuntu-latest
-    steps:
-    - name: Configure AWS credentials
-      uses: aws-actions/configure-aws-credentials@v4
-      with:
-        aws-region: ${{ secrets.AWS_REGION }}
-        role-to-assume: arn:aws:iam::${{ secrets.AWS_ACCOUNT_ID }}:role/github
-    - run: aws sts get-caller-identity
 
   release:
     name: Release?
-    needs: [ caller-identity ]
+    needs: [ verify ]
     permissions:
       contents: write
       pull-requests: write

.github/workflows/pr.yaml

@@ -0,0 +1,31 @@
+name: PR
+
+on:
+  pull_request:
+    branches:
+    - main
+    paths-ignore:
+    - .editorconfig
+    - .gitignore
+    - CHANGELOG.md
+    - LICENSE.md
+    - Makefile
+    - README.md
+
+jobs:
+  verify:
+    name: Verify
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v4
+    - name: Setup Terraform
+      uses: hashicorp/setup-terraform@v3
+      with:
+        terraform_version: "1.10"
+    - name: Initialise with no backend
+      run: terraform init -backend=false
+    - name: Check formatting
+      run: terraform fmt -check -recursive
+    - name: Validate the configuration
+      run: terraform validate