Fix broken opengles dart engine tests that crash with GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT

[b-luk]

Some opengles dart engine tests are currently skipped because they crash with the following error:

[ERROR:flutter/impeller/renderer/backend/gles/blit_command_gles.cc(79)] Break on 'ImpellerValidationBreak' to inspect point of failure: Could not create a complete framebuffer: GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT
[FATAL:flutter/impeller/renderer/backend/gles/blit_pass_gles.cc(88)] Check failed: result. Must be able to encode GL commands without error.

These tests seem to pass when running with an unopt build (e.g. host_debug_unopt_arm64), and crash when running on a non-unopt build (e.g. ci/host_debug_arm64_tests).

The following tests have this behavior:

codec_test.dart
decode_image_from_pixels_sync_test.dart
encoding_test.dart
image_dispose_test.dart
image_resize_test.dart

[b-luk]

This failure behavior is very similar a bunch of tests which originally failed but were fixed as part of #181933.

The fix for those tests was to properly handle the RAII return value of MakeRenderContextCurrent() in a place which wasn't properly handling it before.

See https://github.com/flutter/flutter/pull/181933/changes#r2775519231

It's possible that the still-failing tests are due to other places where we don't properly handle a MakeRenderContextCurrent() return value.