Remove LF_Alpha repository link from repositories.txt #12790

Job	Run time
diff	0s
decline-request	0s
label	0s
parse-fail	0s
decline-submissions	0s
check-submissions-result	0s
not-submission	0s
Check ${{ matrix.submission.submissionURL }}	0s
merge-fail	0s
merge	0s
check-submissions-fail	0s
unexpected-fail	0s
request-review	0s
parse	-5s
	-5s

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