test: style updates for assert.snapshot()

This commit updates the assert.snapshot() fixtures to better
match the code style of the rest of the codebase.

Author: cjihrig

test/fixtures/assert-snapshot/basic.mjs

@@ -1,3 +1,3 @@
 import assert from 'node:assert';
 
-await assert.snapshot("test", "name");
+await assert.snapshot('test', 'name');

test/fixtures/assert-snapshot/multiple.mjs

@@ -1,4 +1,4 @@
 import assert from 'node:assert';
 
-await assert.snapshot("test", "name");
-await assert.snapshot("test", "another name");
+await assert.snapshot('test', 'name');
+await assert.snapshot('test', 'another name');

test/fixtures/assert-snapshot/non-existing-name.mjs

@@ -1,4 +1,4 @@
 import assert from 'node:assert';
 
-await assert.snapshot("test", "another name");
-await assert.snapshot("test", "non existing");
+await assert.snapshot('test', 'another name');
+await assert.snapshot('test', 'non existing');

test/fixtures/assert-snapshot/single.mjs

@@ -1,3 +1,3 @@
 import assert from 'node:assert';
 
-await assert.snapshot("test", "snapshot");
+await assert.snapshot('test', 'snapshot');

test/fixtures/assert-snapshot/value-changed.mjs

@@ -1,3 +1,3 @@
 import assert from 'node:assert';
 
-await assert.snapshot("changed", "snapshot");
+await assert.snapshot('changed', 'snapshot');