Bug 1949784 [wpt PR 50865] - Fix invalid indentation in exception error message, a=testonly

Automatic update from web-platform-tests
Fix invalid indentation in exception error message

The indentation here is important because it changes the correctness of
the YAML snippet.

Bug: 393561071
Change-Id: I7d31f8526a81a9a092b1946415118e486797b6b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6219872
Reviewed-by: Andres Ricardo Perez <andresrperezchromium.org>
Commit-Queue: Jean-Philippe Gravel <jpgravelchromium.org>
Cr-Commit-Position: refs/heads/main{#1423935}

--

wpt-commits: fe3d5bae49e9bc6bcb8462a1f94d7fc855d40c12
wpt-pr: 50865

UltraBlame original commit: 8d7a6fe842f5a96e36eeddb5af389dbaa9dab0dd

Author: marco-c

testing/web-platform/tests/html/canvas/tools/gentest.py

@@ -1011,11 +1011,11 @@ def _get_variant_dimensions(params: _TestParams) -> List[_VariantDimension]:
                 variants:
                 - dimension1-variant1:
                     param: ...
-                    dimension1-variant2:
+                  dimension1-variant2:
                     param: ...
                 - dimension2-variant1:
                     param: ...
-                    dimension2-variant2:
+                  dimension2-variant2:
                     param: ..."""))
 
     variants_layout = params.get('variants_layout',