[WIP] docker: Fix docker image build

[victorges]

What does this pull request do? Explain your changes. (required)
The nasm version was recently upgraded in the indexes, which broke
our ffmpeg build. Apparently ffmpeg has trouble with versions 2.16+ of nasm.

The exact version was determined by running a couple commands on my latest
go-livepeer image build to determine what version of nasm we used to have
before:

cd /home/user/workspace && docker run --rm --entrypoint nasm glp-buildcached -v
NASM version 2.14.02

cd /home/user/workspace && docker run --rm --entrypoint bash glp-buildcached -lc "apt-cache policy nasm | head"
nasm:
  Installed: 2.14.02-1
  Candidate: 2.14.02-1
  Version table:
 *** 2.14.02-1 500
        500 http://archive.ubuntu.com/ubuntu focal/universe amd64 Packages
        100 /var/lib/dpkg/status

We could also fix this by switching to yasm instead of nasm, but I don't even know what
that package does so let's just do the safest thing and stick to the version that worked lol

Specific updates (required)

• Pin nasm version on install
• Mark it as non-upgradable so the rest of the docker build doesn't change it

How did you test each of these updates (required)
Build

Does this pull request close any open issues?
https://discord.com/channels/423160867534929930/1447457162736570461

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[victorges]

Still broken...

[j0sh]

Building the latest NASM should hopefully do the trick: #3825

Yasm is not really maintained anymore and is much slower to assemble.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 31.67957%. Comparing base (1f5b377) to head (f372691).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@              Coverage Diff              @@
##              master       #3832   +/-   ##
=============================================
  Coverage   31.67957%   31.67957%           
=============================================
  Files            159         159           
  Lines          39022       39022           
=============================================
  Hits           12362       12362           
+ Misses         25771       25770    -1     
- Partials         889         890    +1     

see 2 files with indirect coverage changes

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