Add File Input Output in ALGOL 60

[pascalecu]

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I Am Adding a New Code Snippet in an Existing Language

• I fixed Add File Input Output in ALGOL 60 #5742
• I did not include any extra folders/libraries
• I named the pull request using Add {PROJECT} in {LANGUAGE} format

Other notes

The GNU MARST documentation (which is terrible and way too concise) has to say this:

In order to determine the name of a file, which should be assigned to the channel n, the
I/O routine looks for an environment variable named FILE_n. If such variable exists, its
value is used as the filename. Otherwise, its name (i.e. the character string "FILE_n") is
used as the filename.

which is why I changed the testinfo.yml.