fix(manager/terraform): add required_version to preflight content check

lib/manager/terraform/__fixtures__/terraformBlock.tf

@@ -0,0 +1,3 @@
+terraform {
+  required_version = "1.0.0"
+}

lib/manager/terraform/__snapshots__/extract.spec.ts.snap

@@ -390,6 +390,21 @@ Object {
 }
 `;
 
+exports[`manager/terraform/extract extractPackageFile() test terraform block with only requirement_terraform_version 1`] = `
+Object {
+  "deps": Array [
+    Object {
+      "currentValue": "1.0.0",
+      "datasource": "github-tags",
+      "depName": "hashicorp/terraform",
+      "depType": "required_version",
+      "extractVersion": "v(?<version>.*)$",
+      "lineNumber": 1,
+    },
+  ],
+}
+`;
+
 exports[`manager/terraform/extract extractPackageFile() update lockfile constraints with range strategy update-lockfile 1`] = `
 Object {
   "deps": Array [

lib/manager/terraform/extract.spec.ts

@@ -12,6 +12,7 @@ const tf2 = `module "relative" {
 const helm = loadFixture('helm.tf');
 const lockedVersion = loadFixture('lockedVersion.tf');
 const lockedVersionLockfile = loadFixture('rangeStrategy.hcl');
+const terraformBlock = loadFixture('terraformBlock.tf');
 
 const adminConfig: RepoGlobalConfig = {
   // `join` fixes Windows CI
@@ -62,5 +63,16 @@ describe('manager/terraform/extract', () => {
       expect(res.deps).toHaveLength(3);
       expect(res.deps.filter((dep) => dep.skipReason)).toHaveLength(0);
     });
+
+    it('test terraform block with only requirement_terraform_version', async () => {
+      const res = await extractPackageFile(
+        terraformBlock,
+        'terraformBlock.tf',
+        {}
+      );
+      expect(res.deps).toHaveLength(1);
+      expect(res.deps.filter((dep) => dep.skipReason)).toHaveLength(0);
+      expect(res).toMatchSnapshot();
+    });
   });
 });

lib/manager/terraform/extract.ts

@@ -36,6 +36,7 @@ const contentCheckList = [
   'required_providers ',
   ' "helm_release" ',
   ' "docker_image" ',
+  'required_version',
 ];
 
 export async function extractPackageFile(
@@ -45,6 +46,10 @@ export async function extractPackageFile(
 ): Promise<PackageFile | null> {
   logger.trace({ content }, 'terraform.extractPackageFile()');
   if (!checkFileContainsDependency(content, contentCheckList)) {
+    logger.trace(
+      { fileName },
+      'preflight content check has not found any relevant content'
+    );
     return null;
   }
   let deps: PackageDependency<TerraformManagerData>[] = [];