Fix parenthesizing of expressions in view! interpolation syntax

[lukechu10]

Fixes #262

Adds an extra (...) around #splice in packages/sycamore-macro/src/view/element.rs to make sure whole expression is borrowed.

[codecov-commenter]

Codecov Report

Merging #304 (0bf498e) into master (6b739b8) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #304   +/-   ##
=======================================
  Coverage   72.70%   72.70%           
=======================================
  Files          38       38           
  Lines        5143     5143           
=======================================
  Hits         3739     3739           
  Misses       1404     1404           

Impacted Files	Coverage Δ
packages/sycamore-macro/src/view/element.rs	96.36% <100.00%> (ø)

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