Swift 5.3 was released, use it for CI

[tomerd]

motivation: Swift 5.3 was released, use if for CI

changes: update docker setup to use the release version of 5.3

[tomerd]

@swift-server-bot test this please

[tomerd]

@swift-server-bot test this please

[tomerd]

@ktoso tests failed 3 time. flaky, or is this a genuine 5.3 issue?

[yim-lee]

I believe the failure is expected: #746 (comment)

[ktoso]

Yes that's the release compilation failure.

FYI @tomerd
5.3 has broken compilation in release mode on linux when specific mangling happens (and it does for us): [68467435] Swift 5.3-dev compilation broken on Linux #758

We decided to merge and keep moving forward and reported the radar: rdar://68467435 (Linux + Swift 5.3-dev, compiler crash: Demangle.h:199: uint64_t swift::Demangle::Node::getIndex() const: Assertion hasIndex()' failed.)`

The fix has been merged to the 5.3 branch, so I hope 5.3.1 will work again: swiftlang/swift#33962 -- 7 days ago (this PR is 4 days ago), so I think the nightlies should actually work again... I'll test that.

We may have to remain on nightly for now until 5.3.1 is out

[ktoso]

// The nightly Swift 5.3 is ~14 days behind and the fix was merged 7 days ago, so Swift 5.3 nightly still is failing compilation

[ktoso]

So I decided to skip the known-to-fail release compilation requiring integration test #773 since it was adding much noise in all PRs...

We could re-enable it as soon as the nightly docker image ships the fixed build, but in order to move to 5.3-RELEASE we'll need 5.3.1 (same goes for prod users)

[tomerd]

waiting for 5.3.1 seems right to me

[ktoso]

Sounds good, thanks 👍
Stashing this PR then -- okey to keep it open.

[tomerd]

@swift-server-bot test this please

[tomerd]

replaced by #793