Unskip iap_brand example test

[roaks3]

This test was skipped when it was originally introduced with #3135, but no reason was given, and I suspect it was never intended to be skipped. The iap_client uses a very similar test that is working, so I think we should unskip this one as well, and it will validate the docs example.

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• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Generated Terraform providers, and ran make test and make lint in the generated providers to ensure it passes unit and linter tests.
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• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 1 file changed, 69 insertions(+))
Terraform Beta: Diff ( 1 file changed, 69 insertions(+))

[modular-magician]

Tests analytics

Total tests: 0
Passed tests 0
Skipped tests: 0
Affected tests: 0

Errors occurred during REPLAYING mode. Please fix them to complete your PR
View the build log

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 1 file changed, 20 insertions(+), 6 deletions(-))
Terraform Beta: Diff ( 1 file changed, 20 insertions(+), 6 deletions(-))

[modular-magician]

Tests analytics

Total tests: 2706
Passed tests 2420
Skipped tests: 279
Affected tests: 7

Action taken

Found 7 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

TestAccIapBrand_iapBrandExample|TestAccAlloydbCluster_missingLocation|TestAccAlloydbBackup_missingLocation|TestAccApigeeKeystoresAliasesKeyCertFile_apigeeKeystoresAliasesKeyCertFileTestExample|TestAccDataSourceAlloydbLocations_basic|TestAccApigeeKeystoresAliasesPkcs12_ApigeeKeystoresAliasesPkcs12Example|TestAccDataSourceGoogleFirebaseAndroidAppConfig

Get to know how VCR tests work

[modular-magician]

Tests passed during RECORDING mode:
TestAccAlloydbCluster_missingLocation[Debug log]
TestAccAlloydbBackup_missingLocation[Debug log]
TestAccApigeeKeystoresAliasesKeyCertFile_apigeeKeystoresAliasesKeyCertFileTestExample[Debug log]
TestAccDataSourceAlloydbLocations_basic[Debug log]
TestAccApigeeKeystoresAliasesPkcs12_ApigeeKeystoresAliasesPkcs12Example[Debug log]
TestAccDataSourceGoogleFirebaseAndroidAppConfig[Debug log]

Tests failed during RECORDING mode:
TestAccIapBrand_iapBrandExample[Error message] [Debug log]

Please fix these to complete your PR
View the build log or the debug log for each test

[roaks3]

Closing because my assumptions were wrong on this. The test was not being generated, but instead a handwritten test was doing the same job with a slight modification: it ignored diffs with the project field (I believe it receives a project_id but returns a project_number).

I was hoping this was a quick win to simply unskip the test, but since it is more complicated (and the resource is still under test), we should be fine leaving the test as-is, and considering this skip_test: true to be intended.