Fix path resolve for rollup config

[mellyeliu]

Ran into this when trying to run npm i. Similar fix to facebook/stylex#1029

[!] TypeError: The "paths[0]" argument must be of type string. Received undefined
    at new NodeError (node:internal/errors:405:5)
    at validateString (node:internal/validators:162:11)
    at Object.resolve (node:path:1115:7)
    at file:///Users/mellyeliu/react-strict-dom/packages/react-strict-dom/tools/rollup.config.mjs:17:20

[github-actions]

workflow: benchmarks/size

Comparison of minified (terser) and compressed (brotli) size results, measured in bytes. Smaller is better.

Results	Base	Patch	Ratio
react-strict-dom/dist/dom/index.js
· compressed	2,513	2,513	1.00
· minified	8,695	8,695	1.00
react-strict-dom/dist/dom/runtime.js
· compressed	855	855	1.00
· minified	2,435	2,435	1.00
react-strict-dom/dist/native/index.js
· compressed	16,028	16,028	1.00
· minified	59,946	59,946	1.00

[github-actions]

workflow: benchmarks/perf (native)

Comparison of performance test results, measured in operations per second. Larger is better.

Results	Base	Patch	Ratio
css.create
· small	1,148,075	1,139,199	0.99	-
· small with units	438,365	434,159	0.99	-
· small with variables	672,895	666,895	0.99	-
· several small	323,229	318,844	0.99	-
· large	208,014	205,559	0.99	-
· large with polyfills	148,866	144,606	0.97	-
· complex	101,518	100,167	0.99	-
· unsupported	222,969	219,057	0.98	-
css.createTheme
· simple theme	228,428	230,499	1.01	+
· polyfill theme	215,356	214,455	1.00	-
css.props
· small	245,737	246,130	1.00	+
· small with units	192,620	192,096	1.00	-
· small with variables	106,489	106,448	1.00	-
· small with variables of units	75,502	75,510	1.00	+
· large	104,846	104,579	1.00	-
· large with polyfills	37,599	37,565	1.00	-
· complex	23,630	23,578	1.00	-
· unsupported	147,192	146,067	0.99	-
· simple merge	163,589	163,239	1.00	-
· wide merge	17,931	17,940	1.00	+
· deep merge	17,552	17,526	1.00	-
· themed merge	31,618	31,253	0.99	-