Upgrade Elixir to 1.18 on CI etc. #643

Job	Run time
[23.3/1.14.5] new Phoenix app analysed by Credo [OTP/Elixir]	12s
[23.3/1.16.2] new Phoenix app analysed by Credo [OTP/Elixir]	8s
[23.3/1.17.3] new Phoenix app analysed by Credo [OTP/Elixir]	6s
[23.3/1.18.0] new Phoenix app analysed by Credo [OTP/Elixir]	8s
[24.3/1.14.5] new Phoenix app analysed by Credo [OTP/Elixir]	6s
[25.3/1.15.7] new Phoenix app analysed by Credo [OTP/Elixir]	2s
[25.3/1.16.2] new Phoenix app analysed by Credo [OTP/Elixir]	2s
[25.3/1.17.3] new Phoenix app analysed by Credo [OTP/Elixir]	1s
[25.3/1.18.0] new Phoenix app analysed by Credo [OTP/Elixir]	1s
[26.1/1.14.5] new Phoenix app analysed by Credo [OTP/Elixir]	1s
[26.1/1.15.7] new Phoenix app analysed by Credo [OTP/Elixir]	1s
[26.1/1.16.2] new Phoenix app analysed by Credo [OTP/Elixir]	1s
Elixir 1.14.5 OTP 24.3 - v1.6	38s
[26.1/1.17.3] new Phoenix app analysed by Credo [OTP/Elixir]	1s
Elixir 1.15.7 OTP 25.3 - v1.6	34s
Elixir 1.16.2 OTP 25.3 - v1.6	37s
[26.1/1.18.0] new Phoenix app analysed by Credo [OTP/Elixir]	1s
Elixir 1.17.3 OTP 25.3 - v1.6	33s
Elixir 1.18.0 OTP 25.3 - v1.6	36s
Elixir 1.15.7 OTP 26.2 - v1.6	35s
Elixir 1.16.2 OTP 26.2 - v1.6	36s
Elixir 1.17.3 OTP 26.2 - v1.6	35s
Elixir 1.18.0 OTP 26.2 - v1.6	40s
Elixir 1.14.5 OTP 24.3 - main	35s
Elixir 1.15.7 OTP 25.3 - main	36s
Elixir 1.16.2 OTP 25.3 - main	34s
Elixir 1.17.3 OTP 25.3 - main	34s
Elixir 1.18.0 OTP 25.3 - main	39s
Elixir 1.15.7 OTP 26.2 - main	38s
Elixir 1.16.2 OTP 26.2 - main	40s
Elixir 1.17.3 OTP 26.2 - main	37s
Elixir 1.18.0 OTP 26.2 - main	42s
	11m 50s

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