Fix validate-installed-headers test

[michael-wb]

What, How & Why?

The validate-installed-headers test was failing since the query_state.hpp file was using a class without including the file.

☑️ ToDos

• [ ] 📝 Changelog update
• [ ] 🚦 Tests (or not relevant)
• [ ] C-API, if public C++ API changed.

[coveralls-official]

Pull Request Test Coverage Report for Build michael.wilkersonbarker_907

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 218 unchanged lines in 17 files lost coverage.
• Overall coverage decreased (-0.05%) to 91.591%

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Files with Coverage Reduction	New Missed Lines	%
src/realm/aggregate_ops.hpp	1	97.84%
src/realm/util/file.cpp	1	81.73%
src/realm/array_blobs_big.cpp	2	98.72%
src/realm/cluster.cpp	2	80.25%
src/realm/query_expression.hpp	2	93.43%
src/realm/sync/network/websocket.cpp	2	75.36%
src/realm/util/fifo_helper.cpp	2	85.71%
src/realm/uuid.cpp	2	97.06%
test/test_util_network.cpp	3	97.2%
src/realm/sync/network/network.cpp	4	89.86%

Totals
Change from base Build 1796:	-0.05%
Covered Lines:	230718
Relevant Lines:	251899

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💛 - Coveralls