Update agent methods to use the selected R interpreter consistently #3636

Job	Run time
lint / lint	1m 31s
agent / native (macos-latest)	49s
home-view-unit-tests / lint	14s
build / build	1m 47s
agent / native (windows-latest)	1m 28s
agent / native (ubuntu-latest)	49s
vscode / native (macos-latest)	48s
vscode / native (windows-latest)	4m 0s
vscode / native (ubuntu-latest)	1m 28s
package / vscode	2m 26s
archive / archive	42s
bats / native (ubuntu-latest)	2m 26s
vscode-ui	1s
upload	1s
	18m 30s

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