fix(sync_repos): Handle string JSON in VSTS and error dicts in GitLab

[wedamija]

Guard against non-dict exc.json in message_from_error and validate that GitLab search_projects returns project dicts, not error keys.

Fixes SENTRY-5NAY
Fixes SENTRY-5NBH

[sentry]

Bug: The raise_error method may cause an AttributeError by passing a non-dictionary exc.json to error_fields_from_json, which expects a dictionary.
_{Severity: MEDIUM}

Suggested Fix

In the raise_error method, add a check to ensure exc.json is a dictionary before passing it to self.error_fields_from_json. For example: if exc.json and isinstance(exc.json, dict):.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: src/sentry/integrations/base.py#L530-L533

Potential issue: The `raise_error` method calls `self.error_fields_from_json(exc.json)`
if `exc.json` is truthy, but it does not validate that `exc.json` is a dictionary.
Subclasses like `JiraIntegration` and `JiraServerIntegration` implement
`error_fields_from_json` by calling the `.get()` method on the input, assuming it is a
dictionary. If an API returns a non-dictionary JSON response, such as a string,
`exc.json` will be a truthy string. This will cause an `AttributeError` when `.get()` is
called, crashing the integration's error handling logic.

_{Did we get this right? 👍 / 👎 to inform future reviews.}