Bump version to 2.50.0-dev #3768

Job	Run time
Prepare CodeQL unit test matrix	4s
Run unit tests (c, 2.20.7, codeql-cli/v2.20.7, codeql-bundle-v2.20.7, ubuntu-latest-xl, codeql-cl...	33m 56s
Run unit tests (cpp, 2.20.7, codeql-cli/v2.20.7, codeql-bundle-v2.20.7, ubuntu-latest-xl, codeql-...	1h 31m 57s
Validate test results	4s
	2h 6m 1s

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