[flang][driver] Use --match-full-lines in tests for `-test-io`

Use `--match-full-lines` to make sure that FileCheck doesn't match the
output against the `CHECK` lines (which, like other comments, are also
printed).

More specifically, we want to make sure that the following `check` in the
input file:
```
! CHECK: <some-fortran-input>
```
is matched by FileCheck with `<some-fortran-input>` in the generated
output. Without `--match-full-lines`, that check-line will be matched
with `!CHECK:  <some-fortran-input>` instead (which is also
printed together with other contents of the file).

Adding `--match-full-lines` makes the tests stricter and this change
revealed that some `check`s were passing only because that flag was
missing. These are updated accordingly.

Reviewed By: CarolineConcatto, sameeranjoshi

Differential Revision: https://reviews.llvm.org/D90306