Update dependency io.opentelemetry.instrumentation:opentelemetry-instrumentation-bom-alpha to v2.8.0-alpha #2801

Job	Run time
integration-test	7m 24s
build	52s
test (8)	1m 13s
test (11)	1m 0s
test (17)	1m 48s
test (20)	1m 10s
markdown-link-check / markdown-link-check	1m 49s
markdown-lint-check / markdown-lint-check	7s
misspell-check / misspell-check	3s
shell-script-check / shell-script-check	3s
required-status-check	0s
publish-snapshots${{ ((((github.ref_name != 'main') \|\| (github.repository != 'open-telemetry/opentelemetry-java-contrib')) && ' (skipped)') \|\| '') }}	0s
	15m 29s

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