Reinstate the `@Inject` Technology Compatibility Kit (TCK)

[sbrannen]

Since 05ebca8#diff-f3d87c052d0b0574be8982edc194f86f54b56e947d2be49993b36edfd08fc9fe, the SpringAtInjectTckTests test class is no longer public which prevents it from being run as a JUnit 3 test class.

[jhoeller]

Good catch, @sbrannen! Since this affects the 6.1.x line as well, let's consider backporting it.

[sbrannen]

See also commit:

• Include @Inject TCK tests in the build again: 4dc966b