chore: Update .NET Framework Version to 4.8.1 #778

Job	Run time
test-server	22s
test-fake-database	22s
framework (random, no-auth)	4m 1s
core (random, all-features)	38m 40s
framework (controlled, no-auth)	4m 58s
core (random, single-seller)	37m 33s
core (random, no-payment-reconciliation)	37m 41s
core (random, no-auth)	39m 32s
core (random, no-tax-calculation)	36m 54s
core (random, prepayment-always-required)	38m 59s
core (random, facilityuse-has-slots)	39m 25s
core (controlled, all-features)	40m 56s
core (controlled, single-seller)	39m 37s
core (controlled, no-payment-reconciliation)	40m 11s
core (controlled, no-auth)	40m 59s
core (controlled, no-tax-calculation)	38m 50s
core (controlled, prepayment-always-required)	39m 2s
core (controlled, facilityuse-has-slots)	40m 4s
publish-server	0s
deploy-reference-implementation	0s
publish-fake-database	0s
	9h 18m 6s

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