only use rvmsudo if it is on path #13

Job	Run time
Homebrew packaging unit tests	7m 9s
Node.js unit tests on macos-latest	54s
C++ unit tests on macos-latest, as root	9m 30s
Apache 2 integration tests on macos-latest	4m 18s
Node.js unit tests on ubuntu-latest	44s
C++ unit tests on ubuntu-latest, as root	4m 41s
Nginx dynamic module integration tests on macos-latest	3m 19s
Source packaging unit tests	56s
Ruby unit tests on macos-latest	3m 0s
C++ unit tests on macos-latest, as normal-user	4m 26s
Nginx integration tests on macos-latest	2m 46s
Ruby unit tests on ubuntu-latest	3m 28s
Standalone integration tests on macos-latest	4m 58s
C++ unit tests on ubuntu-latest, as normal-user	4m 44s
Apache 2 integration tests on ubuntu-latest	4m 57s
Nginx dynamic module integration tests on ubuntu-latest	4m 43s
Nginx integration tests on ubuntu-latest	4m 20s
Standalone integration tests on ubuntu-latest	5m 25s
	1h 14m 18s

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