Allow configuring CODEQL_THREADS with an env var #9571

Job	Run time
check-codeql-versions	53s
analyze-actions	1m 2s
analyze-javascript (ubuntu-24.04, linked)	4m 9s
analyze-javascript (ubuntu-22.04)	3m 59s
analyze-javascript (ubuntu-24.04)	4m 6s
analyze-javascript (windows-2019)	9m 23s
analyze-javascript (ubuntu-22.04, linked)	3m 50s
analyze-javascript (windows-2019, linked)	6m 33s
analyze-javascript (windows-2022)	8m 33s
analyze-javascript (macos-14, linked)	8m 2s
analyze-javascript (windows-2022, linked)	8m 32s
analyze-javascript (macos-13)	5m 16s
analyze-javascript (macos-14)	4m 56s
analyze-javascript (macos-13, linked)	7m 56s
	1h 17m 10s

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