[CI]: remove arm/v7 from testing

[apostasie]

The corresponding tests serve little to no-purpose (eg: as for adding value specifically for armv7) and are being replaced by equivalent tests against arm64, linux/arm64, linux/arm64/v8.

We do not test any other (s390x, etc) while we could.

Since setting up emulation for arm/v7 is not entirely trivial (because of how tonis image works), suggesting we just get rid of this:

• remove the binfmt contorsions and likelyhood of tests failing locally
• remove the need for an alpine arm v7 availability (important for upcoming work on better controlling test images)
• arm/v7 is going the way of dinosaurs anyhow (even embedded these days gets v8) and our current testing is not doing much anyhow

[AkihiroSuda]

arm/v7 is going the way of dinosaurs anyhow

Not sure about this.
The golang and the OCI ecosystem still supports arm/v7.

[apostasie]

arm/v7 is going the way of dinosaurs anyhow

Not sure about this. The golang and the OCI ecosystem still supports arm/v7.

Sure.
They also support arm/v6 (I think?) - along with s390x, ppc, etc - and we are/should too (by the way, we might want to verify that we can at least build nerdctl for these targets).

I guess the point I would like to outline here is that the tests I am changing here are doing:

• validate that we can run multiple platforms when we have emulation (and we can test that with just arm64, we do not need arm/v7 specifically - we just need a non-native, emulated platform)
• validate that platform name aliasing works (we can do that with linux/arm64/v8 as well) (and also that is probably better suited for unit testing)

I am now wondering if I did not suggest this change earlier actually...
If I did, apologies for that.

Lmk your thoughts (no strong opinion here - just preparing for some CI cleanup)