fix: set isRange true for non-version docker tags

Closes #1806

lib/manager/docker/package.js

@@ -64,7 +64,7 @@ async function getPackageUpdates(config) {
         { currentDepTag },
         'Docker tag is not valid semver - skipping'
       );
-      return upgrades;
+      return upgrades.map(upgrade => ({ ...upgrade, isRange: true }));
     }
     const currentMajor = semver.major(padRange(tagVersion));
     const currentlyStable = isStable(tagVersion, unstablePattern);

test/manager/docker/package.spec.js

@@ -65,6 +65,7 @@ describe('lib/workers/package/docker', () => {
     });
     it('returns a pin', async () => {
       delete config.currentDigest;
+      config.currentTag = 'some-text-tag';
       dockerApi.getDigest.mockReturnValueOnce('sha256:1234567890');
       const res = await docker.getPackageUpdates(config);
       expect(res).toHaveLength(1);