dotnet-8: use offline build (#33140)

Dotnet-8 tag 8.0.10 or older cannot be built anymore, as Microsoft
decided to retire the following repositories:

*
https://pkgs.dev.azure.com/ms/BuildXL/_packaging/BuildXL.Selfhost/nuget/v3/index.json
*
https://pkgs.dev.azure.com/ms/BuildXL/_packaging/BuildXL/nuget/v3/index.json

The repositories were replaced with:

*
https://pkgs.dev.azure.com/mseng/PipelineTools/_packaging/BuildXL.External.Dependencies/nuget/v3/index.json

The problem is that the tagged releases of dotnet <= 8.0.10 will never
be able to build anymore, as tags cannot be replaced.

The fix has landed to dotnet/msbuild#10838, and
the following tagged releases should be buildable again.

See: microsoft/BuildXL#1343

But, if we leverage the offline build, after the prep.sh has been run,
there is no required connection to the inexistent repositories, thus the
build will work for the old tags too.

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Fixes:

Related:

### Pre-review Checklist

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#### For new package PRs only
<!-- remove if unrelated -->
- [ ] This PR is marked as fixing a pre-existing package request bug
- [ ] Alternatively, the PR is marked as related to a pre-existing
package request bug, such as a dependency
- [ ] REQUIRED - The package is available under an OSI-approved or
FSF-approved license
- [ ] REQUIRED - The version of the package is still receiving security
updates
- [ ] This PR links to the upstream project's support policy (e.g.
`endoflife.date`)

#### For new version streams
<!-- remove if unrelated -->
- [ ] The upstream project actually supports multiple concurrent
versions.
- [ ] Any subpackages include the version string in their package name
(e.g. `name: ${{package.name}}-compat`)
- [ ] The package (and subpackages) `provides:` logical unversioned
forms of the package (e.g. `nodejs`, `nodejs-lts`)
- [ ] If non-streamed package names no longer built, open PR to withdraw
them (see [WITHDRAWING
PACKAGES](https://github.com/wolfi-dev/os/blob/main/WITHDRAWING_PACKAGES.md))

#### For package updates (renames) in the base images
<!-- remove if unrelated -->
When updating packages part of base images (i.e.
cgr.dev/chainguard/wolfi-base or ghcr.io/wolfi-dev/sdk)
- [ ] REQUIRED cgr.dev/chainguard/wolfi-base and ghcr.io/wolfi-dev/sdk
images successfully build
- [ ] REQUIRED cgr.dev/chainguard/wolfi-base and ghcr.io/wolfi-dev/sdk
contain no obsolete (no longer built) packages
- [ ] Upon launch, does `apk upgrade --latest` successfully upgrades
packages or performs no actions

#### For security-related PRs
<!-- remove if unrelated -->
- [ ] The security fix is recorded in the
[advisories](https://github.com/wolfi-dev/advisories) repo

#### For version bump PRs
<!-- remove if unrelated -->
- [ ] The `epoch` field is reset to 0

#### For PRs that add patches
<!-- remove if unrelated -->
- [ ] Patch source is documented

---------

Co-authored-by: Dimitri John Ledkov <[email protected]>

Author: ader1990

dotnet-8.yaml

@@ -1,7 +1,7 @@
 package:
   name: dotnet-8
   version: 8.0.10
-  epoch: 0
+  epoch: 1
   description: ".NET SDK"
   copyright:
     - license: MIT
@@ -55,12 +55,13 @@ pipeline:
           ./prep.sh --bootstrap
       #             /p:PrebuiltPackagesPath=/home/build/src/packages \
       - runs: |
-          ./build.sh --online --clean-while-building \
+          ./build.sh --clean-while-building \
             -- \
             /v:n \
             /p:ContinueOnPrebuiltBaselineError=true \
             /p:MinimalConsoleLogOutput=false \
-            /p:SkipPortableRuntimeBuild=true
+            /p:SkipPortableRuntimeBuild=true \
+            /p:BuildWithOnlineSources=false
       - runs: |
           mkdir -p "${{targets.destdir}}"/usr/share/dotnet
           mkdir -p "${{targets.destdir}}"/usr/bin