chore(ci): Remove CI concurrency group & small fixes (#1758)

## Description

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about the "what" this PR is solving -->

It has no effect. The actions are run in parallel anyway. They have been
previously updated to not fail when run in parallel.

## Linked Issues

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## Additional Context

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.github/workflows/update-nix-assets-hash.yaml

@@ -12,9 +12,6 @@ on:
 permissions:
   contents: write
 
-concurrency:
-  group: nix-update
-
 jobs:
   update:
     runs-on: ubuntu-latest

.github/workflows/update-nix-pnpm-deps-hash.yaml

@@ -11,9 +11,6 @@ on:
 permissions:
   contents: write
 
-concurrency:
-  group: nix-update
-
 jobs:
   update:
     runs-on: ubuntu-latest