release-24.2: dev: in doctor, add --sandbox_add_mount_pair if relevant

[blathers-crl]

Backport 1/1 commits from #128207 on behalf of @rickystewart.

/cc @cockroachdb/release

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This was apparently broken with the Bazel 7 upgrade and bazelbuild/bazel#22001 specifically. If --test_tmpdir is set to some directory under /tmp, we need to add /tmp as a mount pair as well. This cannot be done in remote mode so doctor needs to be aware of this.

Closes: #128204
Epic: None
Release note: None
Release justification: Build-only code changes

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Release justification:

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Backports should only be created for serious
  issues or test-only changes.
• Backports should not break backwards-compatibility.
• Backports should change as little code as possible.
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  here).
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  policy.

If your backport adds new functionality, please ensure that the following additional criteria are satisfied:

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters. State changes must be further protected such that nodes running old binaries will not be negatively impacted by the new state (with a mixed version test added).
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  channel (#db-backports-point-releases or #db-backports-XX-X-release) for awareness and discussion.

Also, please add a brief release justification to the body of your PR to justify this
backport.

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is