ghcide test "iface-error-test-1" is flaky

[pepeiborra]

The test has at least 3 failure modes, here is a test run showing all three:

Failure 1: timeout

Interface loading tests
[964](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:964)
    iface-error-test-1:                                                                                   FAIL
[965](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:965)
      Exception: Timed out waiting to receive a message from the server.
[966](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:966)
      Last message received:
[967](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:967)
      {
[968](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:968)
          "method": "window/logMessage",
[969](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:969)
          "params": {
[970](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:970)
              "message": "Live bytes: 0.00MB Heap size: 0.00MB",
[971](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:971)
              "type": 3
[972](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:972)
          },
[973](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:973)
          "jsonrpc": "2.0"
[974](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:974)
      }
[975](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:975)
      Use -p '/iface-error-test-1/' to rerun this test only.

Failure 2: unexpected diagnostics for P.hs:

Interface loading tests
[1042](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:1042)
    iface-error-test-1: FAIL (2.50s)
[1043](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:1043)
      test/exe/Main.hs:6107:
[1044](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:1044)
      Got unexpected diagnostics for Uri {getUri = "file:///tmp/extra-dir-11038963127873/P.hs"} got [Diagnostic {_range = Range {_start = Position {_line = 4, _character = 0}, _end = Position {_line = 4, _character = 3}}, _severity = Just DsWarning, _code = Just (InR "-Wmissing-signatures"), _source = Just "typecheck", _message = "Top-level binding with no type signature: bar :: Int", _tags = Nothing, _relatedInformation = Nothing},Diagnostic {_range = Range {_start = Position {_line = 6, _character = 0}, _end = Position {_line = 6, _character = 3}}, _severity = Just DsWarning, _code = Just (InR "-Wmissing-signatures"), _source = Just "typecheck", _message = "Top-level binding with no type signature: foo :: Bool", _tags = Nothing, _relatedInformation = Nothing},Diagnostic {_range = Range {_start = Position {_line = 4, _character = 0}, _end = Position {_line = 4, _character = 3}}, _severity = Just DsWarning, _code = Just (InR "-Wmissing-signatures"), _source = Just "typecheck", _message = "Top-level binding with no type signature: bar :: Int", _tags = Nothing, _relatedInformation = Nothing},Diagnostic {_range = Range {_start = Position {_line = 6, _character = 0}, _end = Position {_line = 6, _character = 3}}, _severity = Just DsWarning, _code = Just (InR "-Wmissing-signatures"), _source = Just "typecheck", _message = "Top-level binding with no type signature: foo :: Bool", _tags = Nothing, _relatedInformation = Nothing}]

Failure 3: unexpected diagnostics for A.hs:

FAIL (2.54s)
[3100](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:3100)
      test/exe/Main.hs:6107:
[3101](https://github.com/haskell/haskell-language-server/runs/6245281626?check_suite_focus=true#step:8:3101)
      Got unexpected diagnostics for Uri {getUri = "file:///tmp/extra-dir-15590457777873/A.hs"} got []