Update node to v20 (fix Node 16 deprecation) #386

Job	Run time
test-js-project-in-subdir-with-overrides	35s
test-js-project-in-subdir-no-options	35s
test (ubuntu)	34s
test-no-options (ubuntu)	36s
test (macOS)	1m 34s
test-specific-variant	30s
test-no-options (macOS)	1m 56s
test (windows)	1m 34s
test-no-options (windows)	1m 43s
test-specific-volta (1.0.0, macOS)	43s
test-specific-volta (1.0.0, windows)	1m 34s
test-specific-volta-node-npm-yarn (ubuntu)	43s
test-specific-volta (1.0.8, ubuntu)	34s
test-specified-node-npm-yarn-overrides-pinned-versions (ubuntu)	32s
test-specific-volta-node-npm-yarn (macOS)	2m 5s
test-specified-registry-url (ubuntu)	34s
test-specific-volta (1.0.8, macOS)	2m 6s
test-specific-volta-node-npm-yarn (windows)	1m 35s
test-specified-node-npm-yarn-overrides-pinned-versions (macOS)	2m 15s
test-specified-registry-url (macOS)	1m 6s
test-specific-volta (1.0.8, windows)	1m 34s
test-specified-node-npm-yarn-overrides-pinned-versions (windows)	1m 12s
test-specified-registry-url (windows)	1m 33s
test-specific-volta (1.1.0, ubuntu)	30s
test-specific-volta (1.1.0, macOS)	1m 46s
test-specific-volta (1.1.0, windows)	1m 41s
	31m 40s

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